Noa Marom

Tulane University, New Orleans, Louisiana, United States

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Publications (34)140.44 Total impact

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    ABSTRACT: In designing organic materials for electronics applications, particularly for organic photovoltaics (OPV), the ionization potential (IP) of the donor and the electron affinity (EA) of the acceptor play key roles. This makes OPV design an appealing application for computational chemistry since IPs and EAs are readily calculable from most electronic structure methods. Unfortunately reliable, high accuracy wave function methods, such as coupled-cluster theory with single, double, and perturbative triples [CCSD(T)] in the complete basis set (CBS) limit are too expensive for routine applications to this problem for any but the smallest of systems. One solution is to calibrate approximate, less computationally expensive methods against a database of high-accuracy IP/EA values; however, to our knowledge no such database exists for systems related to OPV design. The present work is the first of a multi-part study whose over-arching goal is to determine which computational methods can be used to reliably compute IPs and EAs of electron acceptors. This part introduces a database of 24 known organic electron acceptors and provides high-accuracy vertical IP and EA values expected to be within +/- 0.03 eV of the true non-relativistic, vertical CCSD(T)/CBS limit. Convergence of IP and EA values towards the CBS limit is studied systematically for the Hartree-Fock, MP2 correlation, and beyond-MP2 coupled-cluster contributions to the focal-point estimate.
    Preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    ABSTRACT: The performance of different GW methods is assessed for a set of 24 organic acceptors. Errors are evaluated with respect to coupled cluster singles, doubles, perturbative triples [CCSD(T)] reference data for the vertical ionization potentials (IPs) and electron affinities (EAs), extrapolated to the complete basis set limit. Additional comparisons are made to experimental data, where available. We consider fully self-consistent GW (scGW), partial self-consistency in the Green's function (scGW0), non-self-consistent G0W0 based on several mean-field starting points, and a "beyond GW" second order screened exchange (SOSEX) correction to G0W0. The best performers overall are G0W0+SOSEX and G0W0 based on an IP-tuned long range corrected hybrid functional with the former being more accurate for EAs and the latter for IPs. Both provide a balanced treatment of localized vs. delocalized states and valence spectra in good agreement with photoemission spectroscopy (PES) experiments.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    ABSTRACT: Comparison of ab initio, electron-propagator predictions of vertical ionization potentials and electron affinities of organic, acceptor molecules with benchmark calculations based on the basis-set-extrapolated, coupled-cluster single, double and perturbative triple substitution method has enabled identification of self-energy approximations with mean, unsigned errors between 0.1 and 0.2 eV. Among the self-energy approximations that neglect off-diagonal elements in the canonical, Hartree-Fock orbital basis, the P3 method for electron affinities and the P3+ method for ionization potentials provide the best combination of accuracy and computational efficiency. For approximations that consider the full self-energy matrix, the NR2 methods offer the best performance. The P3+ and NR2 methods successfully identify the correct symmetry label of the lowest cationic state in two cases, naphthalenedione and benzoquinone, where some other methods fail.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    ABSTRACT: The performance of non-empirically tuned long-range corrected hybrid functionals for the prediction of vertical ionization potentials (IPs) and electron affinities (EAs) is assessed for a set of 24 organic acceptor molecules. Basis-set extrapolated coupled cluster singles, doubles, perturbative triples [CCSD(T)] calculations serve as a reference for this study. Compared to standard exchange-correlation functionals, tuned long-range corrected hybrid functionals produce highly reliable results for vertical IPs and EAs, yielding mean absolute errors on par with computationally more demanding GW calculations. In particular, it is demonstrated that tuned long-range corrected hybrid functionals serve as optimal starting points for non-self-consistent GW calculations.
    No preview · Article · Jan 2016 · Journal of Chemical Theory and Computation
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    Dataset: SI TiO2

    Full-text · Dataset · Jul 2015
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    Full-text · Dataset · Jul 2015
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    ABSTRACT: We examine the electronic properties of Sb and F doped SnO2 nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale.
    No preview · Article · Jan 2015 · The Journal of Chemical Physics
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    ABSTRACT: In order to design clusters with desired properties, we have implemented a suite of genetic algorithms tailored to optimize for low total energy, high vertical electron affinity (VEA), and low vertical ionization potential (VIP). Applied to (TiO$_2$)$_n$ clusters, the property-based optimization reveals the underlying structure-property relations and the structural features that may serve as active sites for catalysis. High VEA and low VIP are correlated with the presence of several dangling-O atoms and their proximity, respectively. We show that the electronic properties of (TiO$_2$)$_n$ up to n=20 correlate more strongly with the presence of these structural features than with size.
    Full-text · Article · Jan 2015 · Physical Review B
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    ABSTRACT: Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations.
    No preview · Article · Sep 2014 · The Journal of Chemical Physics
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    ABSTRACT: The efficiency of dye-sensitized solar cells (DSCs) depends critically on the electronic structure of the interfaces in the active region. We employ recently developed dispersion-inclusive density functional theory (DFT) and GW methods to study the electronic structure of TiO2 clusters sensitized with catechol molecules. We show that the energy level alignment at the dye-TiO2 interface is the result of an intricate interplay of quantum size effects and dynamic screening effects and that it may be manipulated by nanostructuring and functionalizing the TiO2. We demonstrate that the energy difference between the catechol LUMO and the TiO2 LUMO, which is associated with the injection loss in DSCs, may be reduced significantly by reducing the dimensions of nanostructured TiO2 and by functionalizing the TiO2 with wide-gap moieties, which contribute additional screening but do not interact strongly with the frontier orbitals of the TiO2 and the dye. Precise control of the electronic structure may be achieved via “interface engineering” in functional nanostructures.Keywords: dye-sensitized solar cell; interface engineering; functional nanostructure; quantum size effect; electronic structure; DFT; GW approximation; dispersion interactions; many-body dispersion; van der Waals
    No preview · Article · Jul 2014 · Journal of Physical Chemistry Letters
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    ABSTRACT: Malaria pigment hemozoin comprises maximally four different hematin anhydride isomeric cyclic dimers, two centrosymmetric (1̅), labeled cd1̅1 and cd1̅2, and two enantiomeric (2), cd2(+) and cd2(−). XRPD refinement yielded two favored crystalline models, one chiral, based on a biochemical hypothesis, comprising mainly cd2(+) and cd1̅1 dimers and the other centrosymmetric made of enantiomorphous crystalline sectors containing the cd1̅1, cd2(+), cd2(−), and cd1̅2 dimers with occupancies ≅ 58:17:17:8.
    No preview · Article · Mar 2014 · Crystal Growth & Design
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    ABSTRACT: Molecular crystals: The structures and relative energies of glycine polymorphs are determined using dispersion corrections to PBE and PBEh density functionals. The picture shows a potential-energy surface for the a-b plane of γ-glycine obtained with density functional theory including many-body dispersion interactions.
    No preview · Article · Jun 2013 · Angewandte Chemie International Edition
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    ABSTRACT: Despite the success of the GW method in describing the photoemission spectra of solids, molecules and clusters, challenges remain. For aromatic molecules for example absolute as well as relative positions of ionisation energies and affinities are not well reproduced in perturbative G0W0 schemes with different starting points as well as in self-consistent GW [1], sometimes even giving the wrong orbital order. Motivated by renormalized second-order perturbation theory [2] for the ground-state energy, we propose a second-order screened exchange correction (SOSEX) to the GW self-energy. This correction follows the spirit of the SOSEX correction to the random-phase approximation for the electron correlation energy and reduces the self-correlation error. The performance of the GW+SOSEX scheme has been benchmarked for a set of molecular systems, including the G2 set, commonly used acceptor molecules, benzene and the azabenzene molecules. We find that the SOSEX correction improves the description of the spectral properties including the orbital order with respect to the different GW schemes, highlighting the importance of reducing the self-correlation error.[4pt] [1] N. Marom et al., arXiv:1211.0416[0pt] [2] X. Ren et al., J. Mater. Sci. 47, 7447 (2012)
    No preview · Article · Mar 2013 · Physical Review B
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    ABSTRACT: The electronic structure of cobalt-phthalocyanine (CoPc) molecules adsorbed on Ag(100) is investigated by photoemission spectroscopy. The results are compared to first-principles electronic structure calculations, based on many-body perturbation theory in the GW approximation. The photoemission data, obtained from both multilayer and monolayer films of CoPc, show that charge transfer occurs between the first molecular layer and the metal surface. Varying the photon energy, to tune the photoionization cross sections, reveals that the charge-transfer-related interface states mainly involve the Co 3d atomic orbitals of the Co central atom. GW calculations for the neutral CoPc molecule and its anion compare well with the experimental observations for a multilayer and a monolayer CoPc film, respectively. They confirm the major role played by the Co atom in the charge-transfer process and elucidate the complex energy rearrangement of the molecular electronic levels upon metal adsorption.
    Full-text · Article · Feb 2013 · Physical review. B, Condensed matter
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    ABSTRACT: Many-body perturbation theory in the GW approximation is a useful method for describing electronic properties associated with charged excitations. A hierarchy of GW methods exists, starting from non-self-consistent G0W0, through partial self-consistency in the eigenvalues and in the Green's function (scGW0), to fully self-consistent GW (scGW). Here, we assess the performance of these methods for benzene, pyridine, and the diazines. The quasiparticle spectra are compared to photoemission spectroscopy (PES) experiments with respect to all measured particle removal energies and the ordering of the frontier orbitals. We find that the accuracy of the calculated spectra does not match the expectations based on their level of self-consistency. In particular, for certain starting points G0W0 and scGW0 provide spectra in better agreement with the PES than scGW.
    Full-text · Article · Dec 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We show that electrodynamic dipolar interactions, responsible for long-range fluctuations in matter, play a significant role in the stability of molecular crystals. Density functional theory calculations with van der Waals interactions determined from a semilocal "atom-in-a-molecule" model result in a large overestimation of the dielectric constants and sublimation enthalpies for polyacene crystals from naphthalene to pentacene, whereas an accurate treatment of non-local electrodynamic response leads to an agreement with the measured values for both quantities. Our findings suggest that collective response effects play a substantial role not only for optical excitations, but also for cohesive properties of non-covalently bound molecular crystals.
    Preview · Article · Nov 2012 · Physical review. B, Condensed matter
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    ABSTRACT: Long-range corrected hybrid functionals that employ a nonempirically tuned range-separation parameter have been demonstrated to yield accurate ionization potentials and fundamental gaps for a wide range of finite systems. Here, we address the question of whether this high level of accuracy is limited to the highest occupied/lowest unoccupied energy levels to which the range-separation parameter is tuned or whether it is retained for the entire valence spectrum. We examine several π-conjugated molecules and find that orbitals of a different character and symmetry require significantly different range-separation parameters and fractions of exact exchange. This imbalanced treatment of orbitals of a different nature biases the resulting eigenvalue spectra. Thus, the existing schemes for the tuning of range-separated hybrid functionals, while providing for good agreement between the highest occupied energy level and the first ionization potential, do not achieve accuracy comparable to reliable G0W0 computations for the entire quasiparticle spectrum.
    Full-text · Article · Nov 2012 · Physical review. B, Condensed matter
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    ABSTRACT: Polymorphs in molecular crystals are often very close in energy, yet they may possess markedly different physical and chemical properties. The understanding and prediction of polymorphism is of paramount importance for a variety of applications, including pharmaceuticals, non-linear optics, and hydrogen storage. Here, we show that the non-additive many-body dispersion (MBD) energy beyond the standard pairwise approximation is crucial for the correct qualitative and quantitative description of polymorphism in molecular crystals. This is rationalized by the sensitive dependence of the MBD energy on the polymorph geometry and the ensuing dynamic electric fields inside molecular crystals. We use the glycine crystal as a fundamental and stringent benchmark case to demonstrate the accuracy of the DFT+MBD method.
    Full-text · Article · Oct 2012
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    Thomas Körzdörfer · Noa Marom
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    ABSTRACT: Many-body perturbation theory in the G0W0 approximation is an increasingly popular tool for calculating electron removal energies and fundamental gaps for molecules and solids. However, the predictive power of G0W0 is limited by its sensitivity to the density functional theory (DFT) starting point. We introduce a nonempirical scheme, which allows us to find a reliable DFT starting point for G0W0 calculations. This is achieved by adapting the amount of Hartree-Fock exchange in a hybrid DFT functional. The G0W0 spectra resulting from this starting point reliably predict experimental photoelectron spectra for a test set of 13 typical organic semiconductor molecules.
    Full-text · Article · Jul 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We propose a new substitutional impurity complex in diamond composed of a lithium atom that is tetrahedrally coordinated by four nitrogen atoms (${\mathrm{LiN}}_{4}$). Density functional calculations are consistent with the hydrogenic impurity model, both supporting the prediction that this complex is a shallow donor with an activation energy of $0.27\ifmmode\pm\else\textpm\fi{}0.06\text{ }\text{ }\mathrm{eV}$. Three paths to the experimental realization of the ${\mathrm{LiN}}_{4}$ complex in diamond are proposed and theoretically analyzed.
    Full-text · Article · May 2012 · Physical Review Letters

Publication Stats

876 Citations
140.44 Total Impact Points

Institutions

  • 2013-2016
    • Tulane University
      • Department of Physics and Engineering Physics
      New Orleans, Louisiana, United States
  • 2011-2014
    • University of Texas at Austin
      • Institute for Computational Engineering and Sciences
      Austin, Texas, United States
  • 2008-2010
    • Weizmann Institute of Science
      • Department of Materials and Interfaces
      Israel