A Primer in Density Functional Theory
Abstract
Density Functionals for Non-relativistic Coulomb Systems in the New Century.- Orbital-Dependent Functionals for the Exchange-Correlation Energy: A Third Generation of Density Functionals.- Relativistic Density Functional Theory.- Time-Dependent Density Functional Theory.- Density Functional Theories and Self-energy Approaches.- A Tutorial on Density Functional Theory.
Chapters (6)
The material world of everyday experience, as studied by chemistry and condensed-matter physics, is built up from electrons
and a few (or at most a few hundred) kinds of nuclei . The basic interaction is electrostatic or Coulombic: An electron at
position r is attracted to a nucleus of charge Z at R by the potential energy −Z/|r − R|, a pair of electrons at r and r′ repel one another by the potential energy 1/|r − r′|, and two nuclei at R and R′ repel one another as Z′Z/|R − R′|. The electrons must be described by quantum mechanics, while the more massive nuclei can sometimes be regarded as classical
particles. All of the electrons in the lighter elements, and the chemically important valence electrons in most elements,
move at speeds much less than the speed of light, and so are non-relativistic.
This chapter is devoted to orbital-dependent exchange-correlation (xc) functionals, a concept that has attracted more and
more attention during the last ten years. After a few preliminary remarks, which clarify the scope of this review and introduce
the basic notation, some motivation will be given why such implicit density functionals are of definite interest, in spite
of the fact that one has to cope with additional complications (compared to the standard xc-functionals). The basic idea of
orbital-dependent xc-functionals is then illustrated by the simplest and, at the same time, most important functional of this
type, the exact exchange of density functional theory (DFT - for a review see e.g. [1], or the chapter by J. Perdew and S. Kurth in this volume).
Contents: 3.1 Summary 3.2 Foundations 3.3 Functionals 3.4 Results 3.5
Further Results
Time-dependent density-functional theory (TDDFT) extends the basic ideas of ground-state density-functional theory (DFT) to
the treatment of excitations and of more general time-dependent phenomena. TDDFT can be viewed as an alternative formulation
of time-dependent quantum mechanics but, in contrast to the normal approach that relies on wave-functions and on the many-body
Schrödinger equation, its basic variable is the one-body electron density, n(r, t). The advantages are clear: The many-body wave-function, a function in a 3N-dimensional space (where N is the number of electrons in the system), is a very complex mathematical object, while the density is a simple function
that depends solely on the 3-dimensional vector r. The standard way to obtain n(r, t) is with the help of a fictitious system of noninteracting electrons, the Kohn-Sham system. The final equations are simple
to tackle numerically, and are routinely solved for systems with a large number of atoms. These electrons feel an effective
potential, the time-dependent Kohn-Sham potential. The exact form of this potential is unknown, and has therefore to be approximated.
One of the fundamental problems in condensed-matter physics and quantum chemistry is the theoretical study of electronic properties.
This is essential to understand the behaviour of systems ranging from atoms, molecules, and nanostructures to complex materials.
Since electrons are governed by the laws of quantum mechanics, the many-electron problem is, in principle, fully described
by a Schrödinger equation (supposing the nuclei to be fixed). However, the electrostatic repulsion between the electrons makes
its numerical resolution an impossible task in practice, even for a relatively small number of particles.
The success of density functional theory (DFT) is clearly demonstrated by the overwhelming amount of research articles describing
results obtained within DFT that were published in the last decades. There is also a fair number of books reviewing the basics
of the theory and its extensions (e.g., the present volume, [1] and [2]). These works fall mainly into three classes: those dealing with the theory (proposing extensions, new functionals, etc.),
those concerned with the technical aspects of the numerical implementations, and others - the vast majority - presenting results.
In our opinion, any scientist working in the field should have a sound knowledge of the three classes. For example, a theorist
developing a new functional should be aware of the difficulties in implementing it. Or the applied scientist, performing calculations
on specific systems, should know the limitations of the theory and of the numerical implementation she/he is using. The goal
of this chapter is to supply the beginner with a brief pedagogical overview of DFT, combining the abovementioned aspects.
However, we will not review its foundations - we redirect the reader to the chapter of J. Perdew and S. Kurth that opens this
book. Obviously, we will not be able to provide many details, but we hope that the beginner obtains a general impression of
the capabilities and limitations of DFT.
... The reason for this is that the scaled wave function Ψ γ is not the ground state of the scaled density n γ . 14 In order to transform density functionals into their spin-polarized equivalents, we use the spin-scaling relations. For the spin-densities n ↑ and n ↓ , the following relation holds: ...
... A large class of functionals are based on the way equation 2.47 is expressed. 14 One way to obtain a canonical definition of xc [n](r) is to go via the so-called adiabatic connection formula. 21 We define the scaled Hamiltonian ...
... The kinetic energy of TF functional, i.e., the first term of equation 2.61 is that of a uniform electron gas. 14 The ground state density can be computed from the Euler-Lagrange equation ...
... For the quantum-mechanical model, he employed a jellium model with uniform electron gas approximation. 22 A jellium model, which describes the positive charge distribution in the electrode as a uniform background charge, is one of the simplest models that accounts for the spillover of electrons into the electrolyte. Although the jellium model does not provide results with highest accuracy, it has been used for work function analyses 29−33 and EDL modeling 34−36 due to its computational efficiency. ...
... This study employs electron energy to account for the effect of a potential-dependent electron spillover. We employ a jellium model with uniform electron gas approximation 22 for its simple and low-cost computation. In the jellium model, positive charges in core atoms of the metal (n m ) are expressed as the uniform background charge, and the density distribution of the valence electrons (n e (x)) is evaluated based on the kinetic and exchangecorrelation energy of electrons with the mean-field approximation. ...
Electric double layers (EDLs) play fundamental roles in various electrochemical processes. Despite the extensive history of EDL modeling, there remain challenges in the accurate prediction of its structure without expensive computation. Herein, we propose a predictive multiscale continuum model of EDL that eliminates the need for parameter fitting. This model computes the distribution of the electrostatic potential, electron density, and species’ concentrations by taking the extremum of the total grand potential of the system. The grand potential includes the microscopic interactions that are newly introduced in this work: polarization of solvation shells, electrostatic interaction in parallel plane toward the electrode, and ion-size-dependent entropy. The parameters that identify the electrode and electrolyte materials are obtained from independent experiments in the literature. The model reproduces the trends in the experimental differential capacitance with multiple electrode and nonadsorbing electrolyte materials (Ag(110) in NaF, Ag(110) in NaClO4, and Hg in NaF), which verifies the accuracy and predictiveness of the model and rationalizes the observed values to be due to changes in electron stability. However, our calculation on Pt(111) in KClO4 suggests the need for the incorporation of electrode/ion-specific interactions. Sensitivity analyses confirmed that effective ion radius, ion valence, the electrode’s Wigner–Seitz radius, and the bulk modulus of the electrode are significant material properties that control the EDL structure. Overall, the model framework and findings provide insights into EDL structures and predictive capability at low computational cost.
... Over the past several decades, these approximations have provided a useful balance between computational cost and accuracy. [3] Although the Kohn-Sham formalism has been used for a variety of chemical/material systems, it suffers from several issues: the XC potential decays too fast at asymptotic internuclear distances, the total energy of the system varies nonlinearly as a function of fractional occupation numbers, the band gaps of periodic systems are underestimated, and unphysical fractional charges appear for stretched internuclear distances (to name a few). [3,4,5] There have been ongoing attempts to obtain better approximations for these XC functionals; however, the inaccuracy of all these Kohn-Sham DFT approaches can be traced to their inherent self-interaction error, which we describe further below. ...
... [3] Although the Kohn-Sham formalism has been used for a variety of chemical/material systems, it suffers from several issues: the XC potential decays too fast at asymptotic internuclear distances, the total energy of the system varies nonlinearly as a function of fractional occupation numbers, the band gaps of periodic systems are underestimated, and unphysical fractional charges appear for stretched internuclear distances (to name a few). [3,4,5] There have been ongoing attempts to obtain better approximations for these XC functionals; however, the inaccuracy of all these Kohn-Sham DFT approaches can be traced to their inherent self-interaction error, which we describe further below. [6] For a one-electron hydrogen atom, the total energy should not have any contributions from electron-electron repulsions, i.e., the E H and E XC energies should exactly cancel each other: E H [ρ α ] + E XC [ρ α , 0] = 0. ...
The accurate prediction of band gaps and structural properties in periodic systems continues to be one of the central goals of electronic structure theory. However, band gaps obtained from popular exchange-correlation functionals (such as LDA and PBE) are severely underestimated partly due to the spurious self-interaction error (SIE) inherent to these functionals. In this work, we present a new formulation and implementation of Wannier function-derived Fermi-L\"{o}wdin (WFL) orbitals for correcting the SIE in periodic systems. Since our approach utilizes a variational minimization of the self-interaction energy with respect to the Wannier charge centers, it is computationally more efficient than the HSE hybrid functional and other self-interaction corrections that require a large number of transformation matrix elements. Calculations on several (17 in total) prototypical molecular solids, semiconductors, and wide-bandgap materials show that our WFL self-interaction correction approach gives better band gaps and bulk moduli compared to semilocal functionals, largely due to the partial removal of self-interaction errors.
... The Density Functional Theory (DFT) is a versatile method describing with very good accuracy the static, dynamic, and thermodynamic properties of many-body quantum systems in a unified framework [1][2][3][4][5][6][7][8]. The success of this approach is due to its relatively low numerical cost compared to the methods that aim to solve under some well-controlled approximations the many-body Schrödinger equation. ...
... where k = k 2 /2 denote the energy of the scattered asymptotic outgoing particle at infinity, i.e. a free particle or plane wave. Diagrammatically, this equation 3,4 can be written as displayed in fig. 9(a) where the propagator G ± 0 (q, ω) = [ω − e q ± iθ] −1 is represented by the solid lines. ...
Over the last two decades, many studies in the Density Functional Theory context revealed new aspects and properties of strongly correlated superfluid quantum systems in numerous configurations that can be simulated in experiments. This was made possible by the generalization of the Local Density Approximation to superfluid systems by Bulgac in [Phys. Rev. C 65, 051305, (2002), Phys. Rev. A 76, 040502, (2007)]. In the presented work, we propose an extension of the Superfluid Local Density Approximation systematically improvable and applicable to a large range of many-body quantum problems getting rid of the fitting procedures of the functional parameters. It turns out that only the knowledge of the density dependence of the quasi-particle properties, namely the chemical potential, the effective mass, and the pairing gap function, are enough to obtain an explicit and accurate local functional of the densities without any adjustment a posterior. This opens the way towards an Effective Field Theory formulation of the Density Functional Theory in the sense that we obtain a universal expansion of the functional parameters entering in the theory as a series in pairing gap function. Finally, we discuss possible applications of the developed approach allowing precise analysis of experimental observations. In that context, we focus our applications on the static structure properties of superfluid vortices.
... It is a pretty popular and practical method, employed extensively by solid-state physicists in ab initio DFT studies to interpret electronic and magnetic interactions in materials and semiconductor materials. Still, LDA has been shown in the literature to yield poor agreements with experimental data for liquid state studies because of the bad treatment of weak interactions [56]. The exchange-correlation energy (E XC [ρ]) for a particle in a uniform electron gas is expressed as: ...
... The second XC category is the GGA, which was introduced to correct the defaults of LDA, notably taking into account the non-uniformity of the electron density. It is also widely used in the solid-state field, and it gives good results for molecular geometries and ground-state energies [56,60]. GGA XC potentials depend not only on the density, but also its first derivative (gradient): The best known within these hybrid functionals are the B3LYP [62] and PBE0 [63] functionals: ...
The nuclear fuel after its dwell time in reactor still bears a substantial amount of recoverable U and Pu. The recovery and purification of these actinides is achieved using a hydro-metallurgical process known as PUREX (Plutonium Uranium Recovering by EXtraction). Based on Liquid-Liquid extraction techniques, this process requires the use of a specific molecule to extract Pu and U, the tri-n-butylphosphate TBP. N,N-dialkylamides (monoamides) are regarded as an alternative family of extractants to TBP, as they are well-known for their strong extraction ability of Pu(IV) and U(VI) elements. In addition to this, they show some interesting features, such as, the strong dependence of the extraction properties (distribution coefficient and selectivity) on the ligands structure as well as chemical conditions. In order to propose the best extracting molecule design for future fuel reprocessing plants, it is crucial to understand the relationship between the structure and the extraction ability. However, the radioactivity of these elements combined with their chemical complexity make the study of these phases experimentally a real challenge. Hence, molecular modeling appears to be the golden solution for getting new insights on this issue.In the first part of this thesis, a relativistic density functional theory study was performed to investigate the influence of the monoamides alkyl chain nature on the relative stability of Pu(IV) complexes. It was possible to reach a better understanding of the strong influence of amide structure on plutonium extraction. For both investigated amide-plutonium-nitrate complexes (inner and outer-sphere complexes), it was found that the introduction of a bulky alkyl group on the carbonyl side has a major impact on the complexation energy. The impact of the polarity of the solution was also investigated and found to be significant.In the second part, within the aim of studying more realistic systems, i.e systems containing long alkyl chains monoamides, heavy elements and other counter ions, and to go beyond the static picture of QM/DFT optimized geometries with molecular dynamics simulations, we have developed a consistent polarizable FF model for the solvent molecules (alkanes, monoamides) based solely on quantum chemical calculations. The chosen ab initio parameterization approach as well as the final force field are presented. Then, the results of molecular dynamics simulations were compared to available experimental macroscopic thermodynamics and structural properties, and show an excellent agreement, making the predictions of properties of pure monoamides reliable. Finally, preliminary MD simulations results for monoamides-dodecane mixtures (DEHiBA/dodecane and DEHBA/dodecane) are presented.
... The most widely used programs today are based on the Kohn-Sham ansatz to original density functional theory [34,128]. The Kohn-Sham ansatz is to replace the original many-body problem by an auxiliary independent-particle system, specifically, it maps the original interacting system with a real potential onto a fictitious non-interacting system whereby the electrons move within an effective Kohn-Sham single-particle potential. ...
... In DFT the electron density n(r) is the principal quantity. The aim of general DFT [34,73,93,128] is to reformulate the quantum mechanical theory in terms of the density instead of the wave function. DFT computational codes are used in practiced to investigate the structural, magnetic and electronic properties of molecules, materials with or without defects. ...
After the first demonstration of graphene, 2D materials have attracted tremendous attention in the electronic devices community. Graphene was regarded as a promising material for electronics due to its extremely high carrier mobility. However, graphene is a semi-metal that does not have a band gap in its pristine form, which makes it inappropriate for switching devices in digital logic circuits. More recently new classes of 2D semiconducting materials, such as Transition Metal Dichalcogenides (TMDs), have been found, and it has been shown that stacking layered materials to get heterostructures is a very powerful method to tailor their properties, mixing them, but also inducing new ones. In this context, this PhD thesis work focused on the electronic properties of monolayers of TMDs, graphene/TMD bilayers, and twisted bilayers of TMDs. In order to study such complex structures, we have combined density functional theory (DFT) approaches and simplified tight-binding (TB) models.The first part of this work is to study theoretically the imperfections in the crystal structure, such as point defects, that can strongly modify the electronic transport properties. We analyse the effect of vacant sites on the density of states, the conductivity, and the mobility of single layers of semiconducting TMDs MX2 (M = Mo, W and X = S, Se, Te). The electronic structure is considered within an eleven band-model, which accounts for the relevant combination of d orbitals of the metal M and p orbitals of the chalcogen X. We use a real-space recursion method (Lanczos method) and the Kubo-Greenwood formula for the calculation of the conductivity in TMDs with different distributions of disorder. Our results show how M or X vacancies create midgap states that localize charge carriers around the defects and modify the transport properties.The second part focuses on the electronic properties of van der Waals heterostructures of graphene/MoS2, graphene/WSe2, and twisted bilayer MoS2 through DFT and TB calculations. Plane-wave pseudopotential DFT calculations were carried out with the ABINIT software package using the generalized gradient approximations and local density approximations for the exchange-correlation potential. In order to obtain precise results, we have fully optimized atomic positions, as well as lattice parameters of all studied heterostructures. First-principles calculations show the effect of the interlayer spacing between the graphene monolayer and the MX2 monolayer on the location of the graphene Dirac cone in the band gap of MX2 semiconductor. We further examine the electronic properties with and without optimization of the atomic positions in different bilayer configurations. For that, we studied graphene/MoS2: 4x4/3x3 [4:3], 5x5/4x4 [5:4], and 9x9/7x7 [9:7], and graphene/WSe2: 4x4/3x3 [4:3] supercell geometries, having different magnitudes of lattice mismatch. It turns out that this mismatch is a key parameter, whereas it has often been forgotten in previous studies. Spin-orbit coupling interaction is also included to see how the strong spin-orbital coupling in MX2 may influence the one of graphene.Finally, we investigate the electronic localization in twisted bilayer MoS2. We propose a new DFT-based Slater-Koster TB model to find the band structure of twisted bilayer MoS2 with small rotation angles theta, where the moiré unit cell becomes too large for DFT computations. This allows the first reliable and systematic studies of such states in twisted bilayer MoS2 for the whole range of rotation angles theta. We show that isolated bands appear at low energy for theta < 5 - 6°. Moreover, these bands become flat bands, characterized by a vanishing average velocity, for the smallest angles theta < 2°, thus confirming the existence of moiré flat bands in twisted bilayer semiconductors, as they exist in twisted bilayer graphene.
... Despite being a fundamental task, solving these equations presents numerical challenges. One challenge arises from the singularities in the external potential near the nucleus, which cause the wavefunctions to vary smoothly between atoms but exhibit sharp changes close to the nucleus [6]. A common approach to addressing numerical challenges in the core region is the use of pseudopotentials [20], where solving the atomic Kohn-Sham equation is crucial. ...
In this paper, we introduce a highly accurate and efficient numerical solver for the radial Kohn--Sham equation. The equation is discretized using a high-order finite element method, with its performance further improved by incorporating a parameter-free moving mesh technique. This approach greatly reduces the number of elements required to achieve the desired precision. In practice, the mesh redistribution involves no more than three steps, ensuring the algorithm remains computationally efficient. Remarkably, with a maximum of 13 elements, we successfully reproduce the NIST database results for elements with atomic numbers ranging from 1 to 92.
... Therefore, some simplification needs to be done. In this work, we will make use of the well-established density functional theory to study 2D materials [13]- [15]. ...
This project aims to utilize Density Functional Theory (DFT) to investigate the elec�tronic band structure of monolayer molybdenum disulfide (MoS2) and molybdenum
diselenide (MoSe2), prominent two- dimensional materials with applications in elec�tronics, optoelectronics, and catalysis. The electronic band structure provides crucial
insights into the material’s electronic properties, including its conductivity, optical
response, and potential for device applications. By employing computational meth�ods, this study seeks to elucidate the fundamental electronic properties of MoS2 &
MoSe2, and contribute to the understanding of its behavior at the atomic scale.
... In this paper, we model the effect of γ-ray irradiation as electronic excitations. We propose a multiscale method for the simulation of the effect of γ-ray irradiation by combining the Monte Carlo simulation of high-energy processes 32,33 and densityfunctional theory (DFT) [34][35][36] calculations of γ-ray-induced excited states. We apply the method to verify the defect-based ISE model of Ref. 29 at the material level and show the necessity of treating electron excitations explicitly. ...
Neutron and γ-ray irradiation damages to transistors are found to be non-additive, and this is denoted as the irradiation synergistic effect (ISE). Its mechanism is not well-understood. The recent defect-based model [Song and Wei, ACS Appl. Electron. Mater. 2, 3783 (2020)] for silicon bipolar junction transistors (BJTs) achieves quantitative agreement with experiments, but its assumptions on the defect reactions are unverified. Going beyond the model requires directly representing the effect of γ-ray irradiation in first-principles calculations, which was not feasible previously. In this work, we examine the defect-based model of the ISE by developing a multiscale method for the simulation of the γ-ray irradiation, where the γ-ray-induced electronic excitations are treated explicitly in excited-state first-principles calculations. We find the calculations agree with experiments, and the effect of the γ-ray-induced excitation is significantly different from the effects of defect charge state and temperature. We propose a diffusion-based qualitative explanation of the mechanism of positive/negative ISE in NPN/PNP BJTs in the end.
... The fundamental quantity that establishes a system's attributes in conventional density functional theory (DFT) is the electron density. In RDFT, extra terms are introduced to the Hamiltonian to take into consideration the effects of relativity on electron motion [8]. ...
Single Perovskite La1-xPbxMnO3
... Many attempts have been made to understand the effect of strain from theoretical perspectives. The electronic properties of semiconductor materials have been previously analyzed by: (a) empirical or semiempirical methods such as the local/nonlocal empirical pseudopotential method [63][64][65][66][67][68][69][70][71], the semi-empirical tight-binding method [72][73][74][75][76][77][78][79][80][81][82][83][84], the k • p method [85][86][87][88][89][90]; or by (b) first-principles methods [91][92][93][94][95][96][97][98] such as density functional theory (DFT) [91,[99][100][101][102][103][104]. Although empirical and semi-empirical methods are computationally efficient and often easy to apply, they rely on many empirical fitting parameters. ...
The modification of the nature and size of bandgaps for III-V semiconductors is of strong interest for optoelectronic applications. Strain can be used to systematically tune the bandgap over a wide range of values and induce indirect-to-direct (IDT), direct-to-indirect (DIT), and other changes in bandgap nature. Here, we establish a predictive first-principles approach, based on density functional theory, to analyze the effect of uniaxial, biaxial, and isotropic strain on the bandgap. We show that systematic variation is possible. For GaAs, DITs were observed at 1.52% isotropic compressive strain and 3.52% tensile strain, while for GaP an IDT was found at 2.63% isotropic tensile strain. We additionally propose a strategy for the realization of direct-indirect transition by combining biaxial strain with uniaxial strain. Further transition points were identified for strained GaSb, InP, InAs, and InSb and compared to the elemental semiconductor silicon. Our analyses thus provide a systematic and predictive approach to strain-induced bandgap tuning in binary III-V semiconductors.
... The Kohn-Sham density functional theory (KSDFT) proposed in 1965 is one of the most successful approximation models towards the computational quantum chemistry, condensed matter physics, etc., for many-body electronic structure calculations [14,32]. Due to the nonlinearity of the governing equation and the complexity of the given electronic structure system, obtaining a high-quality numerical solution has been becoming an important issue in the simulation. ...
In [Dai et al, Multi. Model. Simul., 2020], a structure-preserving gradient flow method was proposed for the ground state calculation in Kohn-Sham density functional theory, based on which a linearized method was developed in [Hu, et al, EAJAM, accepted] for further improving the numerical efficiency. In this paper, a complete convergence analysis is delivered for such a linearized method for the all-electron Kohn-Sham model. Temporally, the convergence, the asymptotic stability, as well as the structure-preserving property of the linearized numerical scheme in the method is discussed following previous works, while spatially, the convergence of the h-adaptive mesh method is demonstrated following [Chen et al, Multi. Model. Simul., 2014], with a key study on the boundedness of the Kohn-Sham potential for the all-electron Kohn-Sham model. Numerical examples confirm the theoretical results very well.
... After this, the improvements have been made to accommodate the entire system [47]. Here, the electron density represents the total energy and the wave function of system. ...
The spherical amorphous silica (a-SiO2) nanoparticles (NPs) are constructed from a previous continuous random network (CRN) model of a-SiO2 with the periodic boundary. The models of radii 12 Å, 15 Å, 18 Å, 20 Å, 22 Å, 24 Å, and 25 Å are built from the CRN structure. Then, three types of models are constructed. Type I has the surface dangling bonds not pacified. In type II models, the dangling bonds are pacified by hydrogen atoms. In type III models, the dangling bonds are pacified by the OH groups. These large models are used to perform the electronic structure calculation of NPs by using the orthogonalized linear combination of atomic orbital (OLCAO) method. The results show some trends in band gap variation for Type I models. The trends in band gap variation for other two types are less clear. A series of NP models with a spherical pore in the middle of a solid NP model are constructed and studied. Spherical pores of radii of 6 Å, 8 Å, 10 Å, 12 Å, 14 Å, 16 Å and 18 Å are introduced within the spherical model of radius 20 Å. After OLCAO calculation, it is found that the band gap values remain constant (5 eV) up to 21.6% porosity and then decreases with increased in porosity. The relation with thickness of the porous NP shell and the surface to volume ratio (S/V) with the calculated band gap are studied in the same manner and will be discussed.
... Thus, the Kohn-Sham equations are also solved iteratively, i.e., through the self-consistency procedure. Since the exact exchange-correlation functional is unknown, there are a great number of approximations for it; detailed reviews on this topic can be found in the books [273][274][275][276][277]. Existing XC functionals can roughly be divided into four groups: the local density approximations (LDAs) [278][279][280], the generalized gradient approximations (GGAs) [281][282][283][284], the hybrid functionals [285,286], and meta-GGA functionals [287]. ...
Quantum chemical methods for the calculation of indirect NMR spin–spin coupling constants and chemical shifts are always in progress. They never stay the same due to permanently developing computational facilities, which open new perspectives and create new challenges every now and then. This review starts from the fundamentals of the nonrelativistic and relativistic theory of nuclear magnetic resonance parameters, and gradually moves towards the discussion of the most popular common and newly developed methodologies for quantum chemical modeling of NMR spectra.
... First, the geometries of the compound considered were entirely optimized at the 6-311+G(d,p) level [68]. In the literature, the B3LYP functional is widely used and leads to dependable results regarding the organic compounds' ground state properties [69]. The calculations for normal modes of vibration were performed using optimized geometries, which led to real frequencies that indicated that these geometries were minimums on the potential energy surfaces. ...
N-(4-((3-Methyl-1,4-dioxo-1,4-dihydronaphthalen-2-yl)selanyl)phenyl)acetamide (5), C19H15NO3Se, was prepared in two steps from 4,4′-diselanediyldianiline (3) via reduction and subsequent nucleophilic reaction with 2-methyl-3-bromo-1,4-naphthalenedione, followed by acetylation with acetic anhydride. The cytotoxicity was estimated against 158N and 158JP oligodendrocytes and the redox profile was also evaluated using different in vitro assays. The technique of single-crystal X-ray diffraction is used to confirm the structure of compound 5. The enantiopure 5 crystallizes in space group P21 with Flack parameter 0.017 (8), exhibiting a chiral layered absolute structure. Molecular structural studies showed that the crystal structure is foremost stabilized by N-H···O and relatively weak C-H···O contacts between molecules, and additionally stabilized by weak C-H···π and Se···N interactions. Hirshfeld surface analysis is used to quantitatively investigate the noncovalent interactions that stabilize crystal packing. Framework energy diagrams were used to graphically represent the stabilizing interaction energies for crystal packing. The analysis of the energy framework shows that the interactions energies of and C-H···π and C-O···π are primarily dispersive and are the crystal’s main important forces. Density functional theory (DFT) calculations were used to determine the compound’s stability, chemical reactivity, and other parameters by determining the HOMO-LUMO energy differences. The determination of its optimized surface of the molecular electrostatic potential (MEP) was also carried out. This study was conducted to demonstrate both the electron-rich and electron-poor sites.
... For an N-particle system by integrating the N-particle distribution probability density function ρ(r 1 , r 2 . r N ) over N −1 variables, as (Carlos, Nogueira and Marques, 2003) ( ) ( , ,..., ) r rr r ...
Density functional theory (DFT) coupled with ) method are carried out to calculate the electronic structures of AgX (X; Br, Cl, and F). The effect of hybridizing between 4d orbital of Ag element and the p orbitals of the X in the valence band plays a very important role in the total density of states configuration. The electronic structure has been studied and all results were compared with the experimental and theoretical values. The importance of this work is that there is insufficient studies of silver halides corresponding the great importance of these compounds. Almost all the results were consistent with the previous studies mentioned here. We found the band gap of AgX to be 2.343 eV, 2.553 eV, and 1.677 eV for AgBr, AgCl, and AgF respectively which are in good agreement with the experimental results.
... Computer simulations that study the structural and transport properties of nanoscale metal-dithiol molecular systems complement the corresponding experimental results. Most of these computational techniques use one, or a combination of methodologies based on density functional theory (DFT) [28], plane waves [29], non-equilibrium Green's function (NEGF) [30], and/or the Landauer-Buttiker formalism [31] that focus on approximating the electronic properties of a structure consisting of a scattering region positioned between two metal electrodes. The transmission and current-voltage (I-V) characteristics of such systems can provide information about the metal-molecular coupling, contact geometry, orbital delocalization and the energy difference between the frontier orbitals, etc. [32][33][34][35]. ...
We report a density functional non-equilibrium Green's function study of the electronic transport properties of nanoscale networks composed of Au metal clusters interconnected with thiolated molecules (1,4-benzenedithiol and 1,3,5-benzenetrithiol), connected in linear chains and branched (Y-, diamond-shaped) extended networks. Calculated current–voltage characteristics of the metal–molecular networks exhibited nonlinearities and rectification with negative differential resistance (NDR) peaks that became more pronounced with increasing chain length. A significant overlap of the energetically close delocalized molecular orbitals near the Fermi energy was observed, which likely combine and contribute to electron transport. The transmission spectra of the linear chains and branched networks showed an increase in the number and width of transmission peaks near the Fermi energy, as the structures were extended, indicating enhanced transmission. Peak-to-valley current NDR ratios as large as ~ 500 and rectification ratios of ~ 10 (0.25 V) were shown for linear and branched circuit elements, respectively, illustrating how charge transport through molecular-scale devices could be controlled with precision by modifying the structure and geometry of molecule–nanoparticle networks. These results provide a potential foundation and building block components for exploring and tailoring applications of metallic nanoparticle-molecular networks in various configurations for nanoelectronic devices and circuits, including memory, logic and sensing.
Graphical Abstract
... Thanks to the seminal works of Hohenberg, Kohn, and Sham 1-3 researchers can simplify the many-body Schrödinger's equation into a mean-field approach for the electronic Hamiltonian in materials. This approach allows us to computationally predict numerous material-specific properties utilizing the elegance of the density-functional theory (DFT) [2][3][4][5][6] . Since the groundbreaking development of DFT, there have been numerous adaptations designed to optimize the accuracy of the exchange and correlation effects in DFT calculations. ...
The density-functional theory is widely used to predict the physical properties of materials. However, it usually fails for strongly correlated materials. A popular solution is to use the Hubbard correction to treat strongly correlated electronic states. Unfortunately, the values of the Hubbard U and J parameters are initially unknown, and they can vary from one material to another. In this semi-empirical study, we explore the U and J parameter space of a group of iron-based compounds to simultaneously improve the prediction of physical properties (volume, magnetic moment, and bandgap). We used a Bayesian calibration assisted by Markov chain Monte Carlo sampling for three different exchange-correlation functionals (LDA, PBE, and PBEsol). We found that LDA requires the largest U correction. PBE has the smallest standard deviation and its U and J parameters are the most transferable to other iron-based compounds. Lastly, PBE predicts lattice parameters reasonably well without the Hubbard correction.
... However, the electrostatic forces between the electrons make its numerical resolution an impossible task in practice, even for a relatively small number of particles or ideal systems. While the analysis of the DFT theory is not the aim of this review, the article, "A Primer in Density Functional Theory" [88] offers a good starting point on this topic. DFT is one of the most common approaches to quantum simulations. ...
During the past decade, pyrolysis routes have been identified as one of the most promising solutions for plastic waste management. However, the industrial adoption of such technologies has been limited and several unresolved blind spots hamper the commercial application of pyrolysis. Despite many years and efforts to explain pyrolysis models based on global kinetic approaches, recent advances in computational modelling such as machine learning and quantum mechanics offer new insights. For example, the kinetic and mechanistic information about plastic pyrolysis reactions necessary for scaling up processes is unravelling. This selective literature review reveals some of the foundational knowledge and accurate views on the reaction pathways, product yields, and other features of pyrolysis created by these new tools. Pyrolysis routes mapped by machine learning and quantum mechanics will gain more relevance in the coming years, especially studies that combine computational models with different time and scale resolutions governed by “first principles.” Existing research suggests that, as machine learning is further coupled to quantum mechanics, scientists and engineers will better predict products, yields, and compositions, as well as more complicated features such as ideal reactor design.
The optimized effective potential (OEP) approach has so far mainly been used in benchmark studies and for the evaluation of band gaps. In this work, we extend the application of the OEP by determining the analytical ionic forces within the plane-wave and pseudopotential framework. It is first shown that, due to the constrained optimization inherent to the OEP approach, an extra term needs to be added to the standard Hellmann-Feynman expression for the forces, whenever nonlocal pseudopotentials are employed. Computing this term for functionals based on Hartree-Fock and the hybrid PBE0 functional yields forces with excellent numerical accuracy. Furthermore, results for equilibrium geometries and vibrational frequencies on a set of molecules and solids confirm that the local exchange OEP is able to reproduce results obtained with the nonlocal exchange potential. Our work opens up the possibility to study lattice dynamics using advanced orbital functionals for describing exchange and correlation effects.
The basis of all molecular property quantum chemical calculations is the correct equilibrium geometry. In this paper, new efficient pecG-n (n = 1, 2) basis sets for the geometry optimization of molecules containing hydrogen and p elements of 2–3 periods are proposed. These basis sets were optimized via the property-energy consistent (PEC) algorithm directed to the minimization of the molecular energy gradient relative to the bond lengths. New basis sets are compact and give equilibrium geometries of very high quality, which is comparable to that provided by considerably larger energy-optimized basis sets. The equilibrium geometries obtained with the pecG-n (n = 1, 2) basis sets and the other basis sets of diverse quality were tested in the CCSD calculations of different second-order molecular properties, including NMR shielding constants, static polarizabilities, and static magnetizabilities. As a result, new basis sets have demonstrated far superior performance as compared to the other energy-optimized basis sets of the same or close sizes commonly used at the geometry optimization stage.
The isomerization of azobenzo-13-crown ether can be expected to be hindered due to the polyoxyethylene linkage connecting the 2,2′-positions of azobenzene. The mixed reference spin-flip time-dependent density functional theory results reveal that the planar and rotational minima of the first photo-excited singlet state (S1) of the trans-isomer pass through a barrier (2.5–5.0 kcal/mol) as it goes toward the torsional conical intersection (S0/S1) geometry (<CNNC ≈ 98°), which is responsible for the cis isomer formation. The second excited singlet state (S2) of the trans form has a nearly planar minimum along the N–N stretching mode, which approaches a sloped S2/S1 intersection geometry. This excited state has a rotational minimum (<CNNC ≈ 99°) as well. Both these minima have a characteristic S2–S1 energy gap of 9 kcal/mol and may undergo internal conversion. A comparison of this system with an analogous 2,2′-dimethoxy-substituted azobenzene system reveals less strain in the rotational path of the latter on the S1 surface, indicating the possibility of its better trans → cis yield than the azocrown. The completely planar S2 geometry of the dimethoxy system has easy access to the linear concerted inversion path, which seems to be the reason behind its reported slightly lower π–π*(S2) yield than n–π*(S1). The thermal cis → trans isomerization path of the azobenzo-13-crown passes through a transition state (frequency 453i cm⁻¹), which corresponds to Gibbs free energy of activation value of 26 kcal/mol in the gas-phase and isooctane. Our study also confirms that its trans isomer strongly binds Li⁺ among the alkali metal ions, and this observation may open up possibilities for practical applications of this azobenzo-crown.
Ultracold atoms provide a platform for analog quantum computer capable of simulating the quantum turbulence that underlies puzzling phenomena like pulsar glitches in rapidly spinning neutron stars. Unlike other platforms like liquid helium, ultracold atoms have a viable theoretical framework for dynamics, but simulations push the edge of current classical computers. We present the largest simulations of fermionic quantum turbulence to date and explain the computing technology needed, especially improvements in the Eigenvalue soLvers for Petaflop Applications(ELPA) library that enable us to diagonalize matrices of record size (millions by millions). We quantify how dissipation and thermalization proceed in fermionic quantum turbulence by using the internal structure of vortices as a new probe of the local effective temperature. All simulation data and source codes are made available to facilitate rapid scientific progress in the field of ultracold Fermi gases.
Description of many-electron systems with a fractional electron number (Ntot) and fractional spin (Mtot) is of great importance in physical chemistry, solid-state physics, and materials science. In this Letter, we provide an exact description of the zero-temperature ensemble ground state of a general, finite, many-electron system and characterize the dependence of the energy and the spin-densities on both Ntot and Mtot, when the total spin is at its equilibrium value. We generalize the piecewise-linearity principle and the flat-plane condition and determine which pure states contribute to the ground-state ensemble. We find a new derivative discontinuity, which manifests for spin variation at a constant Ntot, as a jump in the Kohn–Sham potential. We identify a previously unknown degeneracy of the ground state, such that the total energy and density are unique, but the spin-densities are not. Our findings serve as a basis for development of advanced approximations in density functional theory and other many-electron methods.
Solute-solvent interactions and deprotonation effects have been related to second-order nonlinear optical response modulators. This work takes advantage of sequential Monte Carlo/Quantum mechanics together with Time-Dependent Density Functional Theory, Coupled Cluster methods, and the hyper-Rayleigh scattering formalism to investigate how these effects influence the stability and optical response of p-coumaric acid (pCA) and its anionic and diionic forms. The solvent influences the chromophores in different ways, inducing bathochromic and hypsochromic solvatochromism so for the neutral pCA molecule as for its deprotonated derivatives. The results indicate a high sensitivity of the nonlinear optics (NLO) parameters with relation to proton dissociation. Ionization of the carboxyl group produces the lowest values of the first frequency-dependent hyperpolarizability (\beta_{HRS}), while phenolic deprotonation leads to the highest values. The results show that proton removal can be used as a switch that modulates the NLO response within a wide range of values (159.15 < \beta_{HRS} < 4393.97 au) greater than those reported for reference NLO chromophores like urea (37.3 au) and p-nitroaniline (74.3 au). Thermochemical analysis of enthalpies and Gibbs free energies indicate that both monoionic forms of the pCA molecule are the most stable in gas or water solvents. Furthermore, these structures represent the limits of NLO modulation in the gas and solvent phases. Analysis of the projected density of states and mapping of the molecular electrostatic potential indicate that increased contributions from conduction electrons found in the aromatic ring are the mechanism by which deprotonation enhances the NLO response. All the results show that ionic pCA forms are promising in the functionalization of optoelectronic devices.
Functionalizing single-walled carbon nanotubes (SWNTs) with light-harvesting molecules is a facile way to construct donor-acceptor nanoarchitectures with intriguing optoelectronic properties. Magnesium-centered bacteriochlorin (MgBC), chlorin (MgC), and porphyrin (MgP) are a series of tetrapyrrole macrocycles comprising a central metal and four coordinated aromatic or antiaromatic five-membered rings linked by methine units, which show excellent visible light absorption. To delineate the effects of the aromaticity of coordinated rings on the optoelectronic properties of the nanocomposites, the photoinduced energy and charge transfer dynamics between Mg-centered tetrapyrroles and SWNTs are explored. The results show that excited energy transfer (EET) can occur within MgP@SWNT ascribed to the stabilization of the highest occupied molecular orbital (HOMO) in MgP with the increase of aromatic coordinated rings, while only electron transfer can take place in MgBC@SWNT and MgC@SWNT. Non-adiabatic dynamics simulations demonstrate that electron and hole transfer from MgP to SWNT is asynchronous. The electron transfer is ultrafast with a timescale of ca. 50 fs. By contrast, the hole transfer is significantly suppressed, although it can be accelerated to some extent when using a lower excitation energy of 2.2 eV as opposed to 3.1 eV. Further analysis reveals that the large energy gaps between charge-donor and charge-acceptor states play a crucial role in regulating photoexcited state relaxation dynamics. Our theoretical insights elucidate the structure-functionality interrelations between Mg-centered tetrapyrroles and SWNTs and provide a comprehensive understanding of the underlying charge transfer mechanism within MgP@SWNT nanocomposites, which paves the way for the forthcoming development of SWNT-based photo-related functional materials with targeted applications.
Recently, metal halides have shown great potential for applications such as solar energy harvesting, light emission, and ionizing radiation detection. In this work, we report the preparation, structural, thermal, and...
Compared to conventional silicon-based electronic systems, molecular devices based on spin properties open up a much wider range of possibilities. The use of magnetic molecules as active components in these devices paves the way for the design of new spin-based devices, even controlling single spin centers. For instance, magnetic materials have been proposed as components to build spin valves in which the relative orientation of the magnetization between the electrodes controls the electron transport. Taking advantage of the broad toolkit of chemistry, molecules can be attached to electrodes via linking groups in order to confer robustness to molecule-based devices and increase conductivity. The interest in creating ever more complex molecular devices has been accompanied by significant advances in our theoretical understanding of the electron and spin-transfer phenomenon. The atomistic description of molecular devices is inherently complex due to their increased size in comparison with molecular systems, the combination of components with contrasting electronic structure, and the non-equilibrium nature of the transport problem. Furthermore, the description of spin-polarized systems poses new challenges to the theory, as accurate spin-dependent energetics are difficult to achieve, and the wavefunctions associated with magnetic states can be qualitatively more complex than the closed-shell solutions used for non-magnetic systems. In this chapter, we review molecular-based spintronic devices and the current approaches for modeling electron and spin transport in magnetic systems. Special attention is devoted to systems based on single-molecule magnets (SMMs) and on the emerging interest in the interplay between spin and chirality for the design of new spintronic devices.KeywordsSpintronicsGreen functionsTransmissionMagnetoresistanceChiral-induced spin selectivity
Advances in artificial intelligence (AI) are fueling a new paradigm of discoveries in natural sciences. Today, AI has started to advance natural sciences by improving, accelerating, and enabling our understanding of natural phenomena at a wide range of spatial and temporal scales, giving rise to a new area of research known as AI for science (AI4Science). Being an emerging research paradigm, AI4Science is unique in that it is an enormous and highly interdisciplinary area. Thus, a unified and technical treatment of this field is needed yet challenging. This paper aims to provide a technically thorough account of a subarea of AI4Science; namely, AI for quantum, atomistic, and continuum systems. These areas aim at understanding the physical world from the subatomic (wavefunctions and electron density), atomic (molecules, proteins, materials, and interactions), to macro (fluids, climate, and subsurface) scales and form an important subarea of AI4Science. A unique advantage of focusing on these areas is that they largely share a common set of challenges, thereby allowing a unified and foundational treatment. A key common challenge is how to capture physics first principles, especially symmetries, in natural systems by deep learning methods. We provide an in-depth yet intuitive account of techniques to achieve equivariance to symmetry transformations. We also discuss other common technical challenges, including explainability, out-of-distribution generalization, knowledge transfer with foundation and large language models, and uncertainty quantification. To facilitate learning and education, we provide categorized lists of resources that we found to be useful. We strive to be thorough and unified and hope this initial effort may trigger more community interests and efforts to further advance AI4Science.
In this study, the adsorption of the most common hazardous gases (CO, NO, NO2, and CO2) on the stanene armchair nanoribbon of width 6 (H‐ASnNR(6)) is investigated using density functional theory. The most stable adsorption sites, adsorption energies, charge transfer, electronic features, transmission spectra, and current–voltage analysis are explored. All molecules are physisorbed on H‐ASnNR(6) through van der Waals interactions, indicating a potential use for this material in recoverable gas sensors, and all gas molecules act as acceptors. Additionally, the highest and the lowest charge transfer is related to the NO and CO2 molecules, respectively. It is revealed that the adsorption of NO and NO2 affects the electronic properties of the H‐ASnNR(6), and the system displays conducting behavior, while the influence of CO and CO2 gas molecules on the electrical properties of H‐ASnNR(6) is relatively small. The results demonstrate that compared to pristine H‐ASnNR(6), the transmission function of the gas plus H‐ASnNR(6) system undergoes a significant change, particularly after the adsorption of NO and NO2 molecules. The presence and absence of the molecules are shown by current–voltage (I–V) characteristic results. The results suggest that H‐ASnNR(6) has the potential to be used in gas molecule detection applications.
Solvent effects on the UV-vis spectra of 3-hydroxyflavone and other structurally related molecules (3-hydroxychromen-4-one, 3-hydroxy-4-pyrone, and 4-pyrone) have been studied by combining time-dependent density functional theory (TDDFT) and the polarizable continuum method (PCM). Among the first five excited states of the four considered molecules, electronic states of n → π* and π → π* nature appear. In general, the stability of the n → π* states decreases as the π space becomes larger in such a way that only for 4-pyrone and 3-hydroxy-4-pyrone are they the first excited states. In addition, they become less stabilized in ethanol solution than the ground state, and this causes blueshift transitions in solution. The opposite trend is found for the π → π* excited states. They are less energetic with the π-system size and when passing from gas phase to solution. The solvent shift also depends strongly on the size of the π systems and on the formation of an intramolecular hydrogen bond; thus, it decreases when going from 4-pyrone to 3-hydroxyflavone. The performance of the three versions (cLR, cLR2, and IBSF) of the specific-state PCM method in predicting transition energies are compared.
The electronic and structural properties of the armchair and zigzag single‐walled GaN nanotubes (GaNNTs) are studied by using density functional theory. The effects of tube diameter on the GaN bond lengths, the axial lattice constant, the Fermi energy, the buckling separation, and the bandgap of the tube are investigated. It is revealed that there is a correlation between the bandgap and the buckling; the smaller the bandgap, the higher the buckling. The results show that by increasing diameter of tubes the buckling separation decreases. The 4p‐orbitals of Ga atoms and 2p‐orbitals of N have the main role to the valence band maximum and the conduction band minimum, respectively. All armchair and zigzag GaNNTs are semiconductors having indirect and direct bandgap, respectively. It is also found that by increasing the diameter of nanotubes the bandgap increases, for both armchair and zigzag GaNNTs. The consequences of this study can undoubtedly be useful in future experimental works on optoelectronic devices.
Calculations in Kohn-Sham density functional theory crucially rely on high-quality approximations for the exchange-correlation (xc) functional. Standard local and semi-local approximations fail to predict the ionization potential (IP) and the fundamental gap, departing from the Kohn-Sham orbital energies, due to the deviation of the total energy from piecewise-linearity and the absence of the derivative discontinuity. The ensemble generalization procedure introduced in Phys. Rev. Lett. 110, 126403 (2013) restores, to a large extent, these features in any approximate xc functional and improves its ability to predict the IP and the fundamental gap with negligible additional computational effort. In this work we perform an extensive study of atoms and first ions across the Periodic Table, generalizing the local spin-density and the Perdew-Burke-Ernzerhof approximations. By applying the ensemble generalization to a variety of systems, with s-, p-, and d-character, we assess the accuracy of the method and identify important trends. In particular, we find that the accuracy of our approach heavily depends on the character of the frontier orbitals: when d-orbitals are involved, the performance is far less accurate. Possible sources of error are discussed and ways for further improvement are outlined.
The key idea in Thomas–Fermi theory and its generalizations is the replacement of complicated terms in the kinetic energy and electron–electron repulsion energy contributions to the total energy by relatively simple functionals of the electron density ρ. This chapter first describes Thomas–Fermi theory and then its various generalizations that attempt to correct, with varying success, some of its deficiencies. It concludes with an overview of the Hohenberg–Kohn and Kohn–Sham density functional theories.
Between the ferromagnetic semiconductors of the III‐V group, the transition metals (TMs) doped gallium nitride (Ga, TM)N diluted magnetic semiconductor (DMS) is the most well‐understood and promising applications in spintronic, due to its high Curie temperature. In this research, electronic and magnetic properties of pure armchair (3, 3) and zigzag (5, 0) gallium nitride nanotubes (GaNNTs) and doped with TMs are investigated using the spin‐polarized density functional theory. The spin‐polarized DOS revealed that pure zigzag and armchair GaNNTs are nonmagnetic semiconductors with a direct and indirect bandgap, respectively, in contrast, TMs doped GaNNTs are DMS or half metals (HM). Our results show a high Curie temperature of more than 823 K for Cr and Mn doping, indicating may be good room‐temperature ferromagnetic material for spintronic applications in the future. 11% Cr and Mn atoms doped (3, 3) GaNNT are HM with 100% spin polarization and appear to be good candidates for spintronic applications and especially as spin filter devices. Electronic and magnetic properties of pure gallium nitride nanotubes (GaNNTs) and doped with transition metals (TMs) are investigated using the density functional theory. TMs doped GaNNTs are diluted magnetic semiconductor (DMS) or half metals. Our results show half metal property with a high Curie temperature more than 4940 K for Cr and Mn doping, indicating to be good ferromagnetic material at room‐temperature for spintronic applications in the future.
Magnetic 2D materials have attracted considerable attention for their significant potential application in spintronic. In this work, the effect of substitutional doping of 3d‐transition metals such as Co, Cr, Mn, and Fe on the magnetic and electronic properties of boron nitride nanosheet (BNNS) was studied based on the spin‐polarized density functional theory. The results revealed that the non‐magnetic and semiconducting behavior of BNNS can be altered by magnetically active dopants. The spin‐polarized density of states suggests that pure BNNS is a nonmagnetic semiconductor with a direct bandgap while transition metals doped BNNS are dilute magnetic semiconductors or half metals (HM). Co doping shows the most stable ferromagnetic phases in the nanosheet. A pair of Mn and Co atoms doped BNNS in edge structure show HM property with 100% spin polarization and seem to be good candidates for spintronic applications and especially as spin filter devices and spin current injectors. Effect of substitutional doping of 3d‐transition metals on magnetic and electronic properties of boron nitride nanosheet (BNNS) is studied based on density functional theory. The results revealed that non‐magnetic and semiconducting behavior of BNNS can be altered by magnetically active dopants. Mn and Co doped BNNS show half metal property with 100% spin polarization and seem good candidates for spintronic.
Efficient spatial separation of photogenerated charge carriers across donor/acceptor interfaces has stimulated intense research efforts in photocatalysis fields ascribed to distinctive electronic structure properties of related constituents. Leveraging electronic structure calculations in combination with ab initio-based non-adiabatic carrier dynamics simulations, this study reports ultrafast electron transfer and suppressed nonradiative electron-hole recombination at the interface of PM6/PCBM organic semiconductor heterojunctions, which leads to long-lived charges taking part in hydrogen evolution. The photoinduced dynamical processes are dominantly influenced by energy gaps and non-adiabatic couplings between frontier donor and acceptor states. In addition, hydrogen evolution sites at PM6/PCBM heterojunctions are unveiled by means of first-principles calculations, which suggest that the reaction activity heavily depends on H-adsorbed sites. The activity on the C atoms at the junction of three benzene rings (C666) is much lower than that on the C atoms connected with one pentagon ring and two benzene rings (C665). Nevertheless, the former can be significantly improved via pre-hydrogenating the adjacent C665 atom. This work reveals new photophysical and photochemical properties of PM6/PCBM heterojunctions in detail and provides useful perspectives for performance improvements of photocatalytic materials based on organic donor-acceptor heterojunctions.
One of the most important tasks in the development of high-performance spintronic devices is the preparation of two-dimensional (2D) magnetic layers with long-range exchange interactions. MN4 embedded graphene (MN4−G) layers, with M being transition metal elements, are experimentally accessible 2D layers which exhibit interesting magnetic properties. In this paper, by employing the spin-polarized density functional theory (SP-DFT), we study MN4−G layers with a special focus on the behavior of the indirect M−M exchange interactions and demonstrate that the MN4−G layers with M=Fe, Mn, and Co, are 2D anisotropic magnetic layers with Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. By examining the electronic configurations of the M atoms for various M−M spacers, we demonstrate that the RKKY interaction in such layers are tunable and exhibit an unusual, prolonged decay (r−n, with 0.5≤n≤2). In addition, we isnvestigate the influence of the CuN4 moiety in the graphene host, and show that, in contrary to the other MN4−G layers, the 2D CuN4−G layer behaves as decoupled one-dimensional spin chains, regardless of the spacer lengths.
Through density functional theory (DFT), we investigate the electronic and transport properties of zigzag phosphorene nanoribbons (ZPNRs) and armchair phosphorene nanoribbons (APNRs) passivated with only H or O, or both H and O with different arrangements, systematically. According to the calculated cohesive energies, all structures are stable. Also, the simulation results reveal a semiconductor-to-metal transition in zigzag groups, but all the APNRs are semiconductors. We see the direct-to-indirect energy bandgap transition in armchair groups, while all the semiconductors of zigzag groups have a direct energy bandgap. We also study the effect of external transverse electric field on electronic properties. The applying electric field changes the energy bandgap leading to a semiconductor-to-metal transition at a certain electric field. In addition, the direct-to-indirect bandgap transition and vice versa occurs for some samples. Moreover, edge passivation has a significant effect on transport properties. The breakdown voltage of the devices changes from 0 to 1.94eV, and we observe negative differential resistance (NDR) for some devices. The results indicate that passivated phosphorene nanoribbons are possible, and their properties can effectively be tuned by the arrangement, type of edge atoms, and external electric field, which make these structures a promising candidate for feasible nanodevices.
Theoretical background and fundamental results dealing with the computation of mercury chemical shifts and spin‐spin coupling constants are reviewed with a special emphasis on their stereochemical behavior and applications.
Density matrix electronic structure theory is used in many quantum chemistry methods to "alleviate" the computational cost that arises from directly using wave functions. Although density matrix based methods are computationally more efficient than wave function based methods, significant computational effort is involved. Because the Schrödinger equation needs to be solved as an eigenvalue problem, the time-to-solution scales cubically with the system size in mean-field type approaches such as Hartree-Fock and density functional theory and is solved as many times in order to reach charge or field self-consistency. We hereby propose and study a method to compute the density matrix by using a quadratic unconstrained binary optimization (QUBO) solver. This method could be useful to solve the problem with quantum computers and, more specifically, quantum annealers. Our proposed approach is based on a direct construction of the density matrix using a QUBO eigensolver. We explore the main parameters of the algorithm focusing on precision and efficiency. We show that, while direct construction of the density matrix using a QUBO formulation is possible, the efficiency and precision have room for improvement. Moreover, calculations performed with quantum annealing on D-Wave's new Advantage quantum computer are compared with results obtained with classical simulated annealing, further highlighting some problems of the proposed method. We also suggest alternative methods that could lead to a more efficient QUBO-based density matrix construction.
Finite-temperature Kohn-Sham density functional theory (KS-DFT) is a widely-used method in warm dense matter (WDM) simulations and diagnostics. Unfortunately, full KS-DFT-molecular dynamics models scale unfavourably with temperature and there remains uncertainty regarding the performance of existing approximate exchange-correlation (XC) functionals under WDM conditions. Of particular concern is the expected explicit dependence of the XC functional on temperature, which is absent from most approximations. Average-atom (AA) models, which significantly reduce the computational cost of KS-DFT calculations, have therefore become an integral part of WDM modeling. In this paper, we present a derivation of a first-principles AA model from the fully-interacting many-body Hamiltonian, carefully analyzing the assumptions made and terms neglected in this reduction. We explore the impact of different choices within this model—such as boundary conditions and XC functionals—on common properties in WDM, for example equation-of-state data, ionization degree and the behavior of the frontier energy levels. Furthermore, drawing upon insights from ground-state KS-DFT, we discuss the likely sources of error in KS-AA models and possible strategies for mitigating such errors.
In plasmonics, and particularly in plasmonic photochemistry, the effect of hot‐electron generation is an exciting phenomenon driving new fundamental and applied research. However, obtaining a microscopic description of the hot‐electron states represents a challenging problem, limiting the capability to design efficient nanoantennas exploiting these excited carriers. This paper addresses this limitation and studies the spatial distributions of the photophysical dynamic parameters controlling the local surface photochemistry on a plasmonic nanocrystal. It is found that the generation of energetic electrons and holes in small plasmonic nanocrystals with complex shapes is strongly position‐dependent and anisotropic, whereas the phototemperature across the nanocrystal surface is nearly uniform. The formalism includes three mechanisms for the generation of excited carriers: the Drude process, the surface‐assisted generation of hot‐electrons in the sp‐band, and the excitation of interband d‐holes. The computations show that the hot‐carrier generation originating from these mechanisms reflects the internal structure of hot spots in nanocrystals with complex shapes. The injection of energetic carriers and increased surface phototemperature are driving forces for photocatalytic and photo‐growth processes on the surface of plasmonic nanostructures. Therefore, developing a consistent microscopic theory of such processes is necessary for designing efficient nanoantennas for photocatalytic applications.
Helicobacter pylori is a Gram-negative microaerophilic gastric pathogen, responsible for the cause of peptic ulcer around half of the global population. Although several antibiotics and combination therapies have been employed for H. pylori-related gastric ulcer and cancer regiments, identifying potent inhibitors for specific targets of this bacterium will help assessing better treatment periodicity and methods to eradicate H. pylori. Herein, 1,000,000 natural compounds were virtually screened against Helicobacter pylori Peptide deformylase (HpPDF). Pharmacophore hypotheses were created using ligand and receptor-based pharmacophore modeling of GLIDE. Stringent HTVS and IFD docking protocol of GLIDE predicted leads with stable intermolecular bonds and scores. Molecular dynamics simulation of HpPDF was carried out for 100 ns using GROMACS. Hits ZINC00225109 and ZINC44896875 came up with a glide score of −9.967 kcal/mol and −12.114 kcal/mol whereas; reference compound actinonin produced a glide score of −9.730 kcal/mol. Binding energy values of these hits revealed the involvement of significant Van der Waals and Coulomb forces and the deduction of lipophilic forces that portray the deep hydrophobic residues in the S1pocket of H. pylori. The DFT analysis established the electron density-based features of the molecules and observed that the results correlate with intermolecular docking interactions. Analysis of the MD trajectories revealed the crucial residues involved in HpPDF – ligand binding and the conformational changes in the receptor. We have identified and deciphered the crucial features necessary for the potent ligand binding at catalytic site of HpPDF. The resulting ZINC natural compound hits from the study could be further employed for potent drug development.
Communicated by Ramaswamy H. Sarma
Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.
In this article, Density Functional Theory based calculations, including dispersion corrections, PBE0(D3BJ)/Def2-TZVP(-f), were performed to elucidate the photophysics of the [Ru(bpy)2(HAT)]²⁺ complex in water. In addition, the thermodynamics of the charge and electron transfer excited state reactions of this complex with oxygen, nitric oxide and Guanosine-5'-monophosphate nucleotide (GMP) were investigated. The first singlet excite state, S1, strongly couples with the second and third triplet excited states (T2 and T3) giving rise to a high intersystem crossing rate of 6.26×10¹¹ s⁻¹ which is ∼ 10⁶ greater than the fluorescence rate decay. The thermodynamics of the excited reactions revealed that all electron transfer reactions investigated are highly favorable, due mainly to the high stability of the triply charged radical cation ²PS•3+ species formed after the electron has been transferred. Excited state electron transfer from the GMP nucleotide to the complex is also highly favorable (ΔGsol = -92.6 kcal/mol), showing that this complex can be involved in the photooxidation of DNA, in line with experimental findings. Therefore, the calculations allow to conclude that the [Ru(bpy)2(HAT)]²⁺ complex can act in Photodynamic therapy through both mechanisms type I and II, through electron transfer from and to the complex and triplet-triplet energy transfer, generating ROS, RNOS and through DNA photooxidation. In addition, the work also opens a perspective of using this complex for the in-situ generation of the singlet nitroxyl (¹NO⁻) species, which can have important applications for the generation of HNO and may have, therefore, important impact for physiological studies involving HNO.
In this paper, the ground state Wigner function of a many-body system is explored theoretically and numerically. First, an eigenvalue problem for Wigner function is derived based on the energy operator of the system. The validity of finding the ground state through solving this eigenvalue problem is obtained by building a correspondence between its solution and the solution of stationary Schrödinger equation. Then, a numerical method is designed for solving proposed eigenvalue problem in one dimensional case, which can be briefly described by i) a simplified model is derived based on a quantum hydrodynamic model [Z. Cai et al, J. Math. Chem., 2013] to reduce the dimension of the problem, ii) an imaginary time propagation method is designed for solving the model, and numerical techniques such as solution reconstruction are proposed for the feasibility of the method. Results of several numerical experiments verify our method, in which the potential application of the method for large scale system is demonstrated by examples with density functional theory.
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