Matt Probert

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Verified

Matt verified their affiliation via an institutional email.

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• PhD, BSc, FInstP
• Professor (Full) at University of York

The “egg-box effect” is a known challenge in Density Functional Theory (DFT) calculations which arises from the discretization of continuous quantities, e.g. the electron density. This effect is observed when the system is moved relative to the underlying computational grid and causes an unphysical change in the system’s total energy, violating tra...

Using first principles calculations, we show that \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {Li}_x\hbox {Al}_y\hbox {B}_{2(x+y)}$$\end{document} materials h...

The Hugoniot is the equation of state of a shock-compressed material and is a key part of high-pressure physics. One way of calculating it is via the Hugoniostat that has significant computational advantages over direct calculation via non-equilibrium molecular dynamics. We introduce a number of improvements to the Hugoniostat, which significantly...

There is an urgent need to identify new antiferromagnetic materials that offer a replacement for IrMn alloys for room temperature and above applications. This is driven by the scarcity and high cost of Ir. Recently, MnN with {002} texture grown on a Ta seed layer has been proposed as a cost-effective alternative. However, two key issues need to be...

Thermoelectric materials have the potential to convert waste heat into electricity, but their thermoelectric efficiency must be improved before they are effective and economically viable. One promising route to improving thermoelectric efficiency in thin-film thermoelectric materials is to reduce the material’s thermal conductivity through nanopatt...

Machine learning (ML) methods are of rapidly growing interest for materials modeling, and yet, the use of ML interatomic potentials for new systems is often more demanding than that of established density-functional theory (DFT) packages. Here, we describe computational methodology to combine the CASTEP first-principles simulation software with the...

We have developed a high-throughput computational method to predict the superconducting transition temperature in stable hexagonal M[Formula: see text]AX phases, and applied it to all the known possible choices for M (M: Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Lu, Hf and Ta). We combine this with the best candidates for A (A: Al, Cu, Ge and Sn ) and...

We have developed a high-throughput computational method to predict the superconducting transition temperature in stable hexagonal M2AX phases and applied it to all the known possible choices for M (M: Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Lu, Hf and Ta). We combine this with the best candidates for A (A: Al, Cu, Ge and Sn) and X (X: C and N) from...

The effect of structural relaxations on the magnetocrystalline anisotropy energy (MAE) was investigated by using density functional theory (DFT). The theory of the impact of magnetostructural coupling on the MAE was discussed, including the effects on attempt frequency. The MAE for ferromagnetic FePt (3.45 meV/formula unit) and antiferromagnetic Pt...

A high-throughput computational method is used to predict 39 new superconductors in the Ti-based M2AX phases, and the best candidates are then studied in more detail using density functional theory electron–phonon coupling calculations. The detailed calculations agree with the simple predictions, and Ti2AlX (X: B, C and N) materials are predicted t...

A high-throughput computational method is used to predict 39 new superconductors in the Ti-based M2AX phases, and the best candidates are then studied in more detail using density functional theory electron–phonon coupling calculations. The detailed calculations agree with the simple predictions, and Ti2AlX (X: B, C and N) materials are predicted t...

We present a systematic study of two widely used material structure prediction methods, the Genetic Algorithm and Basin Hopping approaches to global optimization, in a search for the 3 × 3, 5 × 5, and 7 × 7 reconstructions of the Si(111) surface. The Si(111) 7 × 7 reconstruction is the largest and most complex surface reconstruction known, and find...

Progression of computational resources towards exascale computing makes possible simulations of unprecedented accuracy and complexity in the fields of materials and molecular modelling (MMM), allowing high fidelity in silico experiments on complex materials of real technological interest. However, this presents demanding challenges for the software...

The superconducting transition temperatures Tc of hexagonal Nb2AC (A: Al, S, Ge, As and Sn) are investigated using density functional perturbation theory to model the electron-phonon interaction. A critical assessment of the calculated electronic structure and density of states revealed that the electronic states near to the Fermi level are mostly...

Due to the advent of antiferromagnetic (AF) spintronics there is a burgeoning interest in AF materials for a wide range of potential and actual applications. Generally, AFs are characterized via the ordering at the Néel temperature (TN) but, to have a stable AF configuration, it is necessary that the material have a sufficient level of anisotropy s...

Due to the advent of antiferromagnetic (AF) spintronics there is a burgeoning interest in AF materials for a wide range of potential and actual applications. Generally, AFs are characterized via the ordering at the Neel temperature (TN) but, to have a stable AF configuration, it is necessary that the material have a sufficient level of anisotropy s...

The double-helical structure of DNA results from canonical base pairing and stacking interactions. However, variations from steady-state conformations resulting from mechanical perturbations in cells have physiological relevance but their dependence on sequence remains unclear. Here, we use molecular dynamics simulations showing sequence difference...

Previous first-principles calculations have failed to reproduce many of the key thermoelectric features of Fe2VAl, e.g. the maximum values of the Seebeck coefficientSand its asymmetry with respect to the chemical potential. Also, previous theoretical predictions suggested that the pseudo band gap of Fe2VAl switches from indirect to direct upon dopi...

We introduce a number of extensions and enhancements to a genetic algorithm for crystal structure prediction, to make it suitable to study magnetic systems. The coupling between magnetic properties and crystal structure means that it is essential to take a holistic approach, and we present for the first time, a genetic algorithm that performs a sim...

Organic molecular crystals contain long-range dispersion interactions that can be challenging for solid-state methods such as density functional theory (DFT) to capture, and in some industrial sectors are overlooked in favor of classical methods to calculate atomistic properties. Hence, this publication addresses the critical question of whether di...

NbFeSb is a promising thermoelectric material which according to experimental and theoretical studies exhibits a high power factor of up to 10 mW/(m.K^2) at room temperature and ZT of 1 at 1000 K. In all previous theoretical studies, κ_latt is calculated using simplified models, which ignore structural defects. In this work, we calculate κ_latt by...

The double-helical structure of DNA results from canonical base pairing and stacking interactions. However, variations from steady-state conformations result from mechanical perturbations in cells. These different topologies have physiological relevance but their dependence on sequence remains unclear. Here, we use molecular dynamics simulations to...

The double-helical structure of DNA results from canonical base pairing and stacking interactions. However, variations from steady-state conformations result from mechanical perturbations in cells. These different topologies have physiological relevance but their dependence on sequence remains unclear. Here, we use molecular dynamics simulations to...

We present the implementation of dynamical mean-field theory (DMFT) in the CASTEP ab initio code. We explain in detail the theoretical framework for DFT+DMFT and we demonstrate our implementation for three strongly-correlated systems with f-shell electrons: γ-cerium, cerium sesquioxide Ce2O3, and samarium telluride SmTe by using a Hubbard I solver....

We present the implementation of Dynamical Mean-Field Theory (DMFT) in the CASTEP ab-initio code. We explain in detail the theoretical framework for DFT+DMFT and we benchmark our implementation on two strongly-correlated systems with $f$-shell electrons: $\gamma$-cerium and cerium sesquioxide Ce$_{2}$O$_{3}$ by using a Hubbard I solver. We find ver...

We present the results of a theoretical study of H/D diffusion on a Ni(111) surface at a range of temperatures, from 250 K to 75 K. The diffusion is studied using both classical molecular dynamics and the partially adiabatic centroid molecular dynamics method. The calculations are performed with the hydrogen (or deuterium) moving in 3D across a sta...

The solution of the Poisson equation is a crucial step in electronic structure calculations, yielding the electrostatic potential—a key component of the quantum mechanical Hamiltonian. In recent decades, theoretical advances and increases in computer performance have made it possible to simulate the electronic structure of extended systems in compl...

Implicit solvent models provide a simple, yet accurate means to incorporate solvent effects into electronic structure calculations. Such models avoid the computational expense of explicitly modelling solvent molecules by representing the solvent implicitly, for example as a polarizable dielectric medium. In this report, we describe the implementati...

As a common type of structural defects, the grain boundary (GB) plays an important role in tailoring the physical and chemical properties of bulk crystals and their two-dimensional counterparts such as graphene and molybdenum disulfide (MoS2). In this study, we explore the atomic structures and dynamics of three high-symmetry GBs (α, β and γ) in mo...

We present a nanoscale structural and density functional study of the Mn doped 3D topological insulator Bi2Te3. X-ray absorption near edge structure show that Mn has valency of nominally 2+. Extended x-ray absorption fine structure spectroscopy in combination with electron energy loss spectroscopy (EELS) shows that Mn is a substitutional dopant of...

Note: this is just a re-indexing of the paper "Density Functional Theory in the Solid State", Phil. Trans. R. Soc. A 372, 20130270 (2014).

A comparison of DFT methods Density functional theory (DFT) is now routinely used for simulating material properties. Many software packages are available, which makes it challenging to know which are the best to use for a specific calculation. Lejaeghere et al. compared the calculated values for the equation of states for 71 elemental crystals fro...

A systematic study of simulated atomic-resolution electronic energy-loss spectroscopy (EELS) for different graphene nanoribbons (GNRs) is presented. The results of ab initio studies of carbon [Formula: see text] core-loss EELS on GNRs with different ribbon edge structures and different hydrogen terminations show that theoretical core-loss EELS can...

A new class of methods is introduced for solving the Kohn-Sham equations of density functional theory, based on constructing a mapping dynamically between the Kohn-Sham system and an auxiliary system. The resulting auxiliary density functional equation is solved implicitly for the density response, eliminating the instabilities that arise in conven...

Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disu...

These conference proceedings contain the written papers of the contributions presented at the 4th International Conference on Theory, Modelling and Computational Methods for Semiconductor materials and nanostructures. The conference was held at the MediaCityUK, University of Salford, Manchester, UK on 22?24 January 2014. The previous conferences in...

Co-based full Heusler alloys have attracted significant attention due to their high spin polarisation and successful integration as electrodes in magnetic tunnelling junctions and current-perpendicular-to-plane spin valves (CPP-SV)._Further improvement of the CFMS based CPP-SVs requires a fundamental understanding of the effects of atomic disorder...

Density functional theory (DFT) has been used in many fields of the physical sciences, but none so successfully as in the solid state. From its origins in condensed matter physics, it has expanded into materials science, high-pressure physics and mineralogy, solid-state chemistry and more, powering entire computational subdisciplines. Modern DFT si...

In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in...

The melting temperature of solid hydrogen drops with pressure above ~65 GPa, suggesting that a liquid state might exist at low temperatures. It has also been suggested that this low-temperature liquid state might be non-molecular and metallic, although evidence for such behaviour is lacking. Here we report results for hydrogen at high pressures usi...

Experiments and computer simulations have shown that the melting temperature of solid hydrogen drops with pressure above about 65 GPa, suggesting that a low temperature liquid state might exist. It has also been suggested that this liquid state might be non-molecular and metallic, although evidence for such behaviour is lacking. Using a combination...

A combination of state-of-the-art theoretical methods has been used to obtain an atomic-level picture of classical and quantum ordering of protons in cold high-pressure solid hydro-gen. We focus mostly on phases II and III of hydrogen, exploring the effects of quantum nuclear motion on certain features of these phases (through a number of ab initio...

A combination of state-of-the-art theoretical methods has been used to obtain an atomic-level picture of classical and quantum ordering of protons in cold high-pressure solid hydrogen. We focus mostly on phases II and III of hydrogen, exploring the effects of quantum nuclear motion on certain features of these phases (through a number of ab initio...

These conference proceedings contain the written papers of the contributions presented at the 3rd International Conference on Theory, Modelling and Computational Methods for Semiconductor materials and nanostructures. The conference was held at the School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK on 18–20 January 2012...

The relative stability of different crystal structures for pure Fe under applied pressure is calculated from quantum mechanics, using the highly accurate APW+lo method. In the pressure range of 0–100TPa, we corroborate the prediction that iron adopts subsequently the bcc, hcp, fcc, hcp and bcc structures. In contrast to previous studies, we identif...

Atomistic non-equilibrium molecular dynamics simulations of shock wave compression of quartz have been performed using the so-called BKS semi-empirical potential of van Beest, Kramer, and van Santen [Phys. Rev. B 43, 5068 (1991)] to construct the Hugoniot of quartz. Our scheme mimics the real world experimental set up by using a flyer-plate impacto...

Density functional theory can be used to interpret and predict spectroscopic properties of solid-state materials. The relevant computational solutions are usually available in disparate DFT codes, so that it is difficult to use a consistent approach for analyzing various spectroscopic features of a given material. We review the latest developments...

The growth direction and the structure of rare earth silicide nanowires grown on the Si(100) surface have been calculated from first principles. The energies of the optimum structures show that a structure related to the tetragonal bulk phase is more favorable than the hexagonal model and that growth parallel to the dimer rows is lower in energy th...

These conference proceedings contain the written papers of the contributions presented at the 2nd International Conference on: Theory, Modelling and Computational methods for Semiconductors. The conference was held at the St Williams College, York, UK on 13th–15th Jan 2010. The previous conference in this series took place in 2008 at the University...

The hydrogen sorption sites on the surface of holmium silicide grown on Si(111) have been determined using metastable de-excitation spectroscopy, ultraviolet photoemission spectroscopy and density functional theory calculations. Comparison of calculated and measured surface density of states spectra allow us to locate the position of the second sub...

Using ab initio path-integral molecular dynamics, we show that water-hydroxyl overlayers on transition metal surfaces exhibit surprisingly pronounced quantum nuclear effects. The metal substrates serve to reduce the classical proton transfer barriers within the overlayers and, in analogy to ice under high pressure, to shorten the corresponding inte...

It has recently been suggested that a significant amount of Xe can be absorbed in α-quartz and that this might be a significant process in the recycling of Xe from the atmosphere to the interior of the Earth. This suggestion is tested by ab initio calculations of Xe in α-quartz using DFT. Three distinct candidate sites for Xe absorption are identif...

An excited atom spontaneously emitting in a cavity of nanoscale dimensions is known to exhibit the Purcell effect in that it experiences quantifiable changes in its emission rate relative to that in free space. For cavity dimensions below half a radiation wavelength the emission rate is completely suppressed. Although it is generally understood tha...

Existing Genetic Algorithms for crystal structure and polymorph prediction can suffer from stagnation during evolution, with a consequent loss of efficiency and accuracy. An improved Genetic Algorithm (GA) is introduced herein which penalizes similar structures and so enhances structural diversity in the population at each generation. This is shown...

Existing genetic algorithms for crystal structure and polymorph prediction can suffer from stagnation during evolution, with a consequent loss of efficiency and accuracy. An improved genetic algorithm is introduced herein which penalizes similar structures and so enhances structural diversity in the population at each generation. This is shown to i...

We have used Low Energy Electron Diffraction (LEED) I-V analysis and ab initio calculations to quantitatively determine the honeycomb chain model structure for the Si(111)-3x2-Sm surface. This structure and a similar 3x1 recontruction have been observed for many Alkali-Earth and Rare-Earth metals on the Si(111) surface. Our ab initio calculations s...

A nanorod structure has been observed on the Ho/Ge(111) surface using scanning tunneling microscopy (STM). The rods do not require patterning of the surface or defects such as step edges in order to grow as is the case for nanorods on Si(111). At low holmium coverage the nanorods exist as isolated nanostructures while at high coverage they form a p...

The interaction of twisted light beams with nematic liquid crystals is described in terms of Landau's free energy formalism and the uniaxial dielectric model for the liquid crystal. This leads us to a partial differential equation, which is characterized by one position-dependent coefficient, governing the changes in the spatial distribution of the...

A novel Genetic Algorithm is described that is suitable for determining the global minimum energy configurations of crystal structures and which can also be used as a polymorph search technique. This algorithm requires no prior assumptions about unit cell size, shape or symmetry, nor about the ionic configuration within the unit cell. This therefor...

We report results of a first-principles theoretical study of an isolated neutral hydrogen atom in crystalline silicon. Spin-polarised density functional theory is used to treat the electrons, and the path-integral molecular dynamics method is used to describe the quantum properties of the nucleus at finite temperature. This is necessary as the hydr...

The Si(111)3x2-Sm reconstruction that has been observed by STM produces a 3x1 pattern when viewed using LEED [1]. It has been suggested that similar behaviour for Si(111)3x2-Ba is due to the interference of the emergent electron amplitudes between adjacent registry shifted unit cells [2]. We have gathered LEED I(V) curves from this surface and here...

There has been much interest in using genetic algorithms for determining the ground-state structure of clusters [1] and nanowires [2], and more recently silicon surfaces [3]. We present a real-space encoded genetic algorithm which is suitable not only for surface structure calculations, but also for bulk crystal structure determination. This algori...

Rare Earth overlayers on the Si(111) surface have attracted interest due to their novel properties [1,2] and the unusual reconstruction that is formed with a flat rare earth layer buried inside the Silicon [3,4,5,6]. Here we present the results of ab-initio calculations done using the CASTEP [7] code to determine the structural and electronic prope...

A series of phase diagrams is obtained in three dimensions for a smooth pair potential with an outer well and a repulsive inner shoulder. Condensed phase boundaries are located using free energy calculations. Liquid-vapor equilibria are obtained with multicanonical methods. As the depth of the outer well is increased, a simple-hexagonal to close-pa...

A series of phase diagrams is obtained for a smooth pair-potential with an outer well and a repulsive inner shoulder. Condensed phase coexistence curves are located using free-energy calculations. Liquid-vapour equilibria are obtained with multicanonical methods. As the depth of the outer well is increased, a simple-hexagonal to close packed transi...

The method of constant pressure Langevin dynamics is reviewed. The particular utility of the method for ab-initio simulation is discussed. Example results for both semi-empirical and ab-initio systems are given.

The phase behavior of a three-dimensional model substance interacting via a continuous core-softened pair potential is studied. A combination of thermodynamic integration and free-energy augmented metadynamics is employed to identify the ground state structure as simple hexagonal. A transition to close packing is predicted at high pressure. The mel...

The CASTEP code for first principles electronic structure calculations will be described. A brief, nontechnical overview will be given and some of the features and capabilities highlighted. Some features which are unique to CASTEP will be described and near-future development plans outlined.

The stiffness and thermal expansion coefficient of ZrB2 are calculated within the density functional theory formalism. The stiffness tensor obtained here using the static finite strain technique is in good agreement with the results of resonant ultrasonic measurements and points to a possible misinterpretation of the experimentally obtained compres...

Interest in core-softened pair potentials originates in the work of Stell and Hemmer which proposed that such models may produce a liquid-liquid phase transition in a single component system. In this work we concentrate of the `shoulder' form of core-softened potential, constructed as a superposition of the Lennard-Jones potential and an outer Gaus...

The advantages of performing Langevin dynamics in extended systems are discussed. A simple Langevin dynamics scheme for producing the canonical ensemble is reviewed, and is then extended to the Hoover ensemble. We show that the resulting equations of motion generate the isobaric-isothermal ensemble. The Parrinello-Rahman ensemble is then discussed...

The advantages of performing Langevin Dynamics in extended systems are discussed. A simple Langevin Dynamics scheme for producing the canonical ensemble is reviewed, and is then extended to the Hoover ensemble. We show that the resulting equations of motion generate the isobaric-isothermal ensemble. The Parrinello-Rahman ensemble is then discussed...

We present a new algorithm for optimising the configuration of a system of particles using damped molecular dynamics. This new algorithm has a much faster rate of convergence to the ground-state structure than other MD-based schemes. We also show how it is possible to use this algorithm to select dynamically the optimum time step or to precondition...

Molecular dynamics is a popular methodology for investigating the properties of liquids. In this article, the historical development of the subject and its current status will be briefly reviewed. The different parallelisation strategies that are commonly used are discussed, highlighting their relative strengths and weaknesses. Particular attention...

We show how dynamic screening effects on non-equilibrium electron transport can be incorporated in the case of electronically dense GaN-based quantum wells. The theory is based on the Boltzmann equation, leading to evaluations of the momentum relaxation time and, hence, the electron mobility in these heterostructures. We find that both screening an...

We present a systematic methodology for the accurate calculation of defect structures in supercells which we illustrate with a study of the neutral vacancy in silicon. This is a prototypical defect which has been studied extensively using ab initio methods, yet remarkably there is still no consensus about the energy or structure of this defect, or...

The interpretation of a recent molecular dynamics study of equivalent trajectories is questioned. It is shown by a simple counter-example that the observed sudden damping of modes can be explained by a simple dephasing effect due to round-off error, rather than numerical chaos due to coupling terms in the Hamiltonian. The effect can be eliminated b...

First-principles simulation, meaning density-functional theory calculations with plane waves and pseudopotentials, has become a prized technique in condensed-matter theory. Here I look at the basics of the suject, give a brief review of the theory, examining the strengths and weaknesses of its implementation, and illustrating some of the ways simul...

We have performed some simple statistical tests on the recently proposed algorithm for generating normally distributed random numbers and we find that it has some serious flaws with regard to practical application. In particular, we find that there is a statistically significant difference between the sample mean and that expected when using the or...

We present the first ab initio calculations of the internal magnetic field of a molecular magnet using a modified Ewald method. We apply this to both the -phase and -phase forms of the organic radical para-nitrophenyl nitronyl nitroxide (p-NPNN). The -phase is known to exhibit molecular ferromagnetism, whilst the -phase is antiferromagnetic. These...

Ab initio density functional theory calculations for ethanal and muonium, using the projector augmented-wave technique, are described. The potential binding sites for the muonium are evaluated from total-energy-minimization calculations. At these preferred sites the associated (bond-stretching) vibrational frequencies, Einstein coefficients and iso...