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Gustavo E. Scuseria - One of the best experts on this subject based on the ideXlab platform.
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Local Hybrids as a perturbation to global Hybrid Functionals
Journal of Chemical Physics, 2009Co-Authors: Robin Haunschild, Benjamin G. Janesko, Gustavo E. ScuseriaAbstract:We present new local Hybrids of generalized gradient approximation exchange, designed to be small perturbations to the corresponding global Hybrid. In general, local Hybrids include a position-dependent admixture of nonlocal Hartree–Fock exchange. These new local Hybrids incorporate a constant fraction of nonlocal exchange, plus additional nonlocal exchange contributions near nuclei. These Functionals predict molecular thermochemistry and reaction barriers on average more accurately than their “parent” global Hybrid.
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Description of magnetic interactions in strongly correlated solids via range-separated Hybrid Functionals
Physical Review B, 2009Co-Authors: Pablo Rivero, Gustavo E. Scuseria, Ibério De P. R. Moreira, Francesc IllasAbstract:The performance of two range-separated Hybrid (HSE and $\text{LC-}\ensuremath{\omega}\text{PBE}$) exchange-correlation Functionals for describing narrow-band magnetic solids and, more precisely, for predicting magnetic coupling constants has been investigated for a large set of systems for which accurate experimental data exist. The set includes superconducting cuprates parent compounds and transition-metal oxides and fluorides exhibiting a broad range of magnetic coupling values. Both HSE and $\text{LC-}\ensuremath{\omega}\text{PBE}$ provide an overall improvement over the description arising from standard Hybrid Functionals such as the well-known B3LYP. Nevertheless, the two range-separated Hybrid Functionals still overestimate antiferromagnetic and ferromagnetic interactions although significantly less than B3LYP. The increased accuracy of $\text{LC-}\ensuremath{\omega}\text{PBE}$ suggests that the approximations and exact constraints included in the definition of this long-range corrected Hybrid functional have important consequences for the accurate description of exchange and correlation effects of the electronic structure of magnetic solids and other systems exhibiting localized spins.
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screened Hybrid density Functionals for solid state chemistry and physics
Physical Chemistry Chemical Physics, 2009Co-Authors: Benjamin G. Janesko, Thomas M Henderson, Gustavo E. ScuseriaAbstract:Density functional theory incorporating Hybrid exchange–correlation Functionals has been extraordinarily successful in providing accurate, computationally tractable treatments of molecular properties. However, conventional Hybrid Functionals can be problematic for solids. Their nonlocal, Hartree–Fock-like exchange term decays slowly and incorporates unphysical features in metals and narrow-bandgap semiconductors. This article provides an overview of our group’s work on designing Hybrid Functionals for solids. We focus on the Heyd–Scuseria–Ernzerhof screened Hybrid functional [J. Chem. Phys. 2003, 118, 8207], its applications to the chemistry and physics of solids and surfaces, and our efforts to build upon its successes.
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reliability of range separated Hybrid Functionals for describing magnetic coupling in molecular systems
Journal of Chemical Physics, 2008Co-Authors: Pablo Rivero, Ibério De P. R. Moreira, Francesc Illas, Gustavo E. ScuseriaAbstract:The performance of the Heyd–Scuseria–Ernzerhorf (HSE) and single parameter long-range corrected Perdew–Burke–Ernzerhorf (LC-ωPBE) range-separated Hybrids for predicting magnetic coupling constants has been investigated for a broad set of magnetic molecular systems for which accurate experimental data exist. The set includes the H–He–H model system, two organic diradicals with different magnetic behaviors, and a series of Cu dinuclear complexes with a broad range of magnetic coupling values. Both HSE and LC-ωPBE provide a significant improvement to standard Hybrids such as the well-known Hybrid Becke-3-parameters exchange with Lee–Yang–Parr correlation (B3LYP) functional. Nevertheless, the performance of these two range-separated Hybrid Functionals is different: HSE overestimates antiferromagnetic and ferromagnetic interactions in Cu dinuclear complexes (although significantly less than B3LYP), whereas LC-ωPBE treats ferro- and antiferromagnetic couplings on a much more balanced way. The increased accuracy...
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self consistent generalized kohn sham local Hybrid Functionals of screened exchange combining local and range separated Hybridization
Journal of Chemical Physics, 2008Co-Authors: Benjamin G. Janesko, Aliaksandr V Krukau, Gustavo E. ScuseriaAbstract:We present local Hybrid Functionals that incorporate a position-dependent admixture of short-range (screened) nonlocal exact [Hartree-Fock-type (HF)] exchange. We test two limiting cases: screened local Hybrids with no long-range HF exchange and long-range-corrected local Hybrids with 100% long-range HF exchange. Long-range-corrected local Hybrids provide the exact asymptotic exchange-correlation potential in finite systems, while screened local Hybrids avoid the problems inherent to long-range HF exchange in metals and small-bandgap systems. We treat these Functionals self-consistently using the nonlocal exchange potential constructed from Kohn-Sham orbital derivatives. Generalized Kohn-Sham calculations with screened and long-range-corrected local Hybrids can provide accurate molecular thermochemistry and kinetics, comparable to existing local Hybrids of full-range exchange. Generalized Kohn-Sham calculations with existing full-range local Hybrids provide results consistent with previous non-self-consistent and “localized local Hybrid” calculations. These new Functionals appear to provide a promising extension of existing local and range-separated Hybrids.
Jeanluc Bredas - One of the best experts on this subject based on the ideXlab platform.
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description of the charge transfer states at the pentacene c60 interface combining range separated Hybrid Functionals with the polarizable continuum model
Journal of Physical Chemistry Letters, 2016Co-Authors: Zilong Zheng, Jeanluc Bredas, Veaceslav CoropceanuAbstract:Density functional theory (DFT) approaches based on range-separated Hybrid Functionals are currently methods of choice for the description of the charge-transfer (CT) states in organic donor/acceptor solar cells. However, these calculations are usually performed on small-size donor/acceptor complexes and as result do not account for electronic polarization effects. Here, using a pentacene/C60 complex as a model system, we discuss the ability of long-range corrected (LCR) Hybrid Functionals in combination with the polarizable continuum model (PCM) to determine the impact of the solid-state environment on the CT states. The CT energies are found to be insensitive to the interactions with the dielectric medium when a conventional time-dependent DFT/PCM (TDDFT/PCM) approach is used. However, a decrease in the energy of the CT state in the framework of LRC Functionals can be obtained by using a smaller range-separated parameter when going from an isolated donor/acceptor complex to the solid-state case.
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theoretical study of the local and charge transfer excitations in model complexes of pentacene c60 using tuned range separated Hybrid Functionals
Journal of Chemical Theory and Computation, 2014Co-Authors: Cairong Zhang, John S Sears, Bing Yang, Saadullah G Aziz, Veaceslav Coropceanu, Jeanluc BredasAbstract:The characteristics of the electronic excited states and the charge-transfer processes at organic–organic interfaces play an important role in organic electronic devices. However, charge-transfer excitations have proven challenging to describe with conventional density functional theory (DFT) methodologies due to the local nature of the exchange-correlation potentials often employed. Here, we examine the excited states of model pentacene-C60 complexes using time-dependent DFT with, on one hand, one of the most popular standard Hybrid Functionals (B3LYP) and, on the other hand, several long-range corrected Hybrid Functionals for which we consider both default and nonempirically tuned range-separation parameters. The DFT results based on the tuned Functionals are found to agree well with the available experimental data. The results also underline that the interface geometry of the complex has a strong effect on the energies and ordering of the singlet and triplet charge-transfer states.
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organic electronic materials recent advances in the dft description of the ground and excited states using tuned range separated Hybrid Functionals
Accounts of Chemical Research, 2014Co-Authors: Thomas Korzdorfer, Jeanluc BredasAbstract:ConspectusDensity functional theory (DFT) and its time-dependent extension (TD-DFT) are powerful tools enabling the theoretical prediction of the ground- and excited-state properties of organic electronic materials with reasonable accuracy at affordable computational costs. Due to their excellent accuracy-to-numerical-costs ratio, semilocal and global Hybrid Functionals such as B3LYP have become the workhorse for geometry optimizations and the prediction of vibrational spectra in modern theoretical organic chemistry. Despite the overwhelming success of these out-of-the-box Functionals for such applications, the computational treatment of electronic and structural properties that are of particular interest in organic electronic materials sometimes reveals severe and qualitative failures of such Functionals. Important examples include the overestimation of conjugation, torsional barriers, and electronic coupling as well as the underestimation of bond-length alternations or excited-state energies in low-band...
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assessment of the performance of tuned range separated Hybrid density Functionals in predicting accurate quasiparticle spectra
Physical Review B, 2012Co-Authors: Thomas Korzdorfer, Noa Marom, John S Sears, Robert M Parrish, David C Sherrill, Jeanluc BredasAbstract: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 \ensuremath{\pi}-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 ${G}_{0}$${W}_{0}$ computations for the entire quasiparticle spectrum.
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long range corrected Hybrid Functionals for π conjugated systems dependence of the range separation parameter on conjugation length
Journal of Chemical Physics, 2011Co-Authors: Thomas Korzdorfer, John S Sears, Christopher Sutton, Jeanluc BredasAbstract:Long-range corrected (range-separated Hybrid) Functionals represent a relatively new class of Functionals for generalized Kohn-Sham theory that have proven to be very successful, for instance, when it comes to predicting ionization potentials and energy gaps for a wide range of molecules and solids. The results obtained from long-range corrected density functional theory approaches can be improved dramatically, if the range-separation parameter (ω) is optimized for each system separately. In this work, we have optimized ω for a series of π-conjugated molecular systems of increasing length by forcing the resulting Functionals to obey the ionization potential-theorem, i.e., that their highest occupied eigenvalue be equal to the ΔSCF ionization potential. The optimized ω values are observed to vary substantially from their default values for the Functionals. For highly conjugated chains such as oligoacenes and polyenes, we find that the characteristic length scale of the range-separation, i.e., 1/ω, grows al...
Matthias Ernzerhof - One of the best experts on this subject based on the ideXlab platform.
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Erratum: “Hybrid Functionals based on a screened Coulomb potential” [J. Chem. Phys. 118, 8207 (2003)]
The Journal of Chemical Physics, 2006Co-Authors: Jochen Heyd, Gustavo E. Scuseria, Matthias ErnzerhofAbstract:Hybrid density Functionals are very successful in describing a wide range of molecular properties accurately. In large molecules and solids, however, calculating the exact (Hartree-Fock) exchange is computationally expensive, especially for systems with metallic characteristics. In the present work, we develop a new Hybrid density functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodynamic properties of molecules are comparable in quality to the most widely used Hybrid Functionals. In addition, we present results of periodic boundary condition calculations for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree-Fock exchange enables fast and accurate Hybrid calculations, even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential Hybrid, combined with its computational advantages, makes it widely applicable to large molecules and periodic systems. (C) 2003 American Institute of Physics.
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local Hybrid Functionals
Journal of Chemical Physics, 2003Co-Authors: Juanita Jaramillo, Gustavo E. Scuseria, Matthias ErnzerhofAbstract:We present a novel approach for constructing Hybrid Functionals by using a local mix of regular density functional theory (DFT) exchange and exact Hartree–Fock (HF) exchange. This local Hybrid approach is computationally feasible for a wide range of molecules. In this work, the local mix of HF and DFT exchange is driven by the ratio of τW=|∇ρ|2/8ρ, the Weizsacker kinetic energy density, with τ, the exact kinetic energy density. This particular choice of local mix yields 100% of exact exchange in one-electron regions. Dissociation energy curves, binding energies, and equilibrium geometries for two-center, three-electron symmetric radical cations can be modeled accurately using this scheme. We also report encouraging results for reaction energy barriers, and somewhat disappointing atomization energies for the small G2 set.
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Hybrid Functionals based on a screened Coulomb potential
The Journal of Chemical Physics, 2003Co-Authors: Jochen Heyd, Gustavo E. Scuseria, Matthias ErnzerhofAbstract:Hybrid density Functionals are very successful in describing a wide range of molecular properties accurately. In large molecules and solids, however, calculating the exact (Hartree–Fock) exchange is computationally expensive, especially for systems with metallic characteristics. In the present work, we develop a new Hybrid density functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodynamic properties of molecules are comparable in quality to the most widely used Hybrid Functionals. In addition, we present results of periodic boundary condition calculations for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree–Fock exchange enables fast and accurate Hybrid calculations, even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential Hybrid, combined with its computational advantages, makes it widely applica...
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Local Hybrid Functionals
Journal of Chemical Physics, 2003Co-Authors: Juanita Jaramillo, Gustavo E. Scuseria, Matthias ErnzerhofAbstract:We present a novel approach for constructing Hybrid Functionals by using a local mix of regular density functional theory (DFT) exchange and exact Hartree–Fock (HF) exchange. This local Hybrid approach is computationally feasible for a wide range of molecules. In this work, the local mix of HF and DFT exchange is driven by the ratio of τW = ∣∇ρ∣2/8ρ, the Weizsäcker kinetic energy density, with τ, the exact kinetic energy density. This particular choice of local mix yields 100% of exact exchange in one-electron regions. Dissociation energy curves, binding energies, and equilibrium geometries for two-center, three-electron symmetric radical cations can be modeled accurately using this scheme. We also report encouraging results for reaction energy barriers, and somewhat disappointing atomization energies for the small G2 set. © 2003 American Institute of Physics. © 2003 American Institute of Physics
Martin Kaupp - One of the best experts on this subject based on the ideXlab platform.
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Development and Implementation of Excited-State Gradients for Local Hybrid Functionals.
Journal of Chemical Theory and Computation, 2019Co-Authors: Robin Grotjahn, Filipp Furche, Martin KauppAbstract:Local Hybrid Functionals are a relatively recent class of exchange-correlation Functionals that use a real-space dependent admixture of exact exchange. Here, we present the first implementation of time-dependent density functional theory excited-state gradients for these Functionals. Based on the ansatz of a fully variational auxiliary Lagrangian of the excitation energy, the working equations for the case of a local Hybrid functional are deduced. For the implementation, we derive the third-order functional derivatives used in the hyper-kernel and kernel-gradients following a seminumerical integration scheme. The first assessment for a test set of small molecules reveals competitive performance for excited-state structural parameters with typical mean absolute errors (MAEs) of 1.2 pm (PBE0: 1.4 pm) for bond lengths as well as for vibrational frequencies with typical MAEs of 81 cm-1 (PBE0: 76 cm-1). Excellent performance was found for adiabatic triplet excitation energies with typical MAEs of 0.08 eV (PBE0: 0.32 eV). In a detailed case analysis of the first singlet and triplet excited states of formaldehyde the conceptional (dis-)advantages of the local Hybrid scheme for excited-state gradients are exposed.
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new approaches for the calibration of exchange energy densities in local Hybrid Functionals
Physical Chemistry Chemical Physics, 2016Co-Authors: Toni M Maier, Alexei V Arbuznikov, Matthias Haasler, Martin KauppAbstract:The ambiguity of exchange-energy densities is a fundamental challenge for the development of local Hybrid Functionals, or of other Functionals based on a local mixing of exchange-energy densities. In this work, a systematic construction of semi-local calibration functions (CFs) for adjusting the exchange-energy densities in local Hybrid Functionals is provided, which directly links a given CF to an underlying semi-local exchange functional, as well as to the second-order gradient expansion of the exchange hole. Using successive steps of integration by parts allows the derivation of correction terms of increasing order, resulting in more and more complicated but also more flexible CFs. We derive explicit first- and second-order CFs (pig1 and pig2) based on B88 generalized-gradient approximation (GGA) exchange, and a first-order CF (tpig1) based on τ-dependent B98 meta-GGA exchange. We combine these CFs with different long-range damping functions and evaluate them for calibration of LDA, B88 GGA, and TPSS meta-GGA exchange-energy densities. Based on a minimization of unphysical nondynamical correlation contributions in three noble-gas dimer potential-energy curves, free parameters in the CFs are optimized, and performance of various approaches in the calibration of different exchange-energy densities is compared. Most notably, the second-order pig2 CF provides the largest flexibility with respect to the diffuseness of the damping function. This suggests that higher-order CFs based on the present integration-by-parts scheme may be particularly suitable for the flexible construction of local Hybrid Functionals.
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Validation of local Hybrid Functionals for TDDFT calculations of electronic excitation energies
Journal of Chemical Physics, 2016Co-Authors: Toni M Maier, Alexei V Arbuznikov, Hilke Bahmann, Martin KauppAbstract:The first systematic evaluation of local Hybrid Functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local Hybrid Functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local Hybrids exhibit comparable performance to standard global or range-separated Hybrid Functionals for common singlet valence excitations, but several local Hybrids outperform all other Functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows that local Hybrids can also provide excellent Rydberg and core excitations, in the latter case rivaling specialized Functionals optimized specifically for such excitations. This good performance of local Hybrids for different excitation types could be traced to relatively large exact-exchange (EXX) admixtures in a spatial region intermediate between valence and asymptotics, as well as close to the nucleus, and lower EXX admixtures in the valence region. In contrast, the tested local Hybrids cannot compete with the best range-separated Hybrids for intra- and intermolecular CT excitation energies. Possible directions for improvement in the latter category are discussed. As the used efficient TDDFT implementation requires essentially the same computational effort for global and local Hybrids, applications of local Hybrid Functionals to excited-state problems appear promising in a wide range of fields. Influences of current-density dependence of local kinetic-energy dependent local Hybrids, differences between spin-resolved and "common" local mixing functions in local Hybrids, and the effects of the Tamm-Dancoff approximation on the excitation energies are also discussed.
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validation of local Hybrid Functionals for tddft calculations of electronic excitation energies
Journal of Chemical Physics, 2016Co-Authors: Toni M Maier, Alexei V Arbuznikov, Hilke Bahmann, Martin KauppAbstract:The first systematic evaluation of local Hybrid Functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local Hybrid Functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local Hybrids exhibit comparable performance to standard global or range-separated Hybrid Functionals for common singlet valence excitations, but several local Hybrids outperform all other Functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows ...
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four component relativistic density functional theory calculations of epr g and hyperfine coupling tensors using Hybrid Functionals validation on transition metal complexes with large tensor anisotropies and higher order spin orbit effects
Journal of Physical Chemistry A, 2015Co-Authors: Sebastian Gohr, Peter Hrobarik, Michal Repiský, Stanislav Komorovský, Kenneth Ruud, Martin KauppAbstract:The four-component matrix Dirac–Kohn–Sham (mDKS) implementation of EPR g- and hyperfine A-tensor calculations within a restricted kinetic balance framework in the ReSpect code has been extended to Hybrid Functionals. The methodology is validated for an extended set of small 4d1 and 5d1 [MEXn]q systems, and for a series of larger Ir(II) and Pt(III) d7 complexes (S = 1/2) with particularly large g-tensor anisotropies. Different density Functionals (PBE, BP86, B3LYP-xHF, PBE0-xHF) with variable exact-exchange admixture x (ranging from 0% to 50%) have been evaluated, and the influence of structure and basis set has been examined. Notably, Hybrid Functionals with an exact-exchange admixture of about 40% provide the best agreement with experiment and clearly outperform the generalized-gradient approximation (GGA) Functionals, in particular for the hyperfine couplings. Comparison with computations at the one-component second-order perturbational level within the Douglas–Kroll–Hess framework (1c-DKH), and a scali...
Thomas Korzdorfer - One of the best experts on this subject based on the ideXlab platform.
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accurate ionization potentials and electron affinities of acceptor molecules ii non empirically tuned long range corrected Hybrid Functionals
Journal of Chemical Theory and Computation, 2016Co-Authors: Lukas Gallandi, Noa Marom, Patrick Rinke, Thomas KorzdorferAbstract: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, and 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 long-range corrected Hybrid Functionals serve as ideal starting points for non-self-consistent GW calculations.
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organic electronic materials recent advances in the dft description of the ground and excited states using tuned range separated Hybrid Functionals
Accounts of Chemical Research, 2014Co-Authors: Thomas Korzdorfer, Jeanluc BredasAbstract:ConspectusDensity functional theory (DFT) and its time-dependent extension (TD-DFT) are powerful tools enabling the theoretical prediction of the ground- and excited-state properties of organic electronic materials with reasonable accuracy at affordable computational costs. Due to their excellent accuracy-to-numerical-costs ratio, semilocal and global Hybrid Functionals such as B3LYP have become the workhorse for geometry optimizations and the prediction of vibrational spectra in modern theoretical organic chemistry. Despite the overwhelming success of these out-of-the-box Functionals for such applications, the computational treatment of electronic and structural properties that are of particular interest in organic electronic materials sometimes reveals severe and qualitative failures of such Functionals. Important examples include the overestimation of conjugation, torsional barriers, and electronic coupling as well as the underestimation of bond-length alternations or excited-state energies in low-band...
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assessment of the performance of tuned range separated Hybrid density Functionals in predicting accurate quasiparticle spectra
Physical Review B, 2012Co-Authors: Thomas Korzdorfer, Noa Marom, John S Sears, Robert M Parrish, David C Sherrill, Jeanluc BredasAbstract: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 \ensuremath{\pi}-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 ${G}_{0}$${W}_{0}$ computations for the entire quasiparticle spectrum.
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long range corrected Hybrid Functionals for π conjugated systems dependence of the range separation parameter on conjugation length
Journal of Chemical Physics, 2011Co-Authors: Thomas Korzdorfer, John S Sears, Christopher Sutton, Jeanluc BredasAbstract:Long-range corrected (range-separated Hybrid) Functionals represent a relatively new class of Functionals for generalized Kohn-Sham theory that have proven to be very successful, for instance, when it comes to predicting ionization potentials and energy gaps for a wide range of molecules and solids. The results obtained from long-range corrected density functional theory approaches can be improved dramatically, if the range-separation parameter (ω) is optimized for each system separately. In this work, we have optimized ω for a series of π-conjugated molecular systems of increasing length by forcing the resulting Functionals to obey the ionization potential-theorem, i.e., that their highest occupied eigenvalue be equal to the ΔSCF ionization potential. The optimized ω values are observed to vary substantially from their default values for the Functionals. For highly conjugated chains such as oligoacenes and polyenes, we find that the characteristic length scale of the range-separation, i.e., 1/ω, grows al...
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Single-particle and quasiparticle interpretation of Kohn-Sham and generalized Kohn-Sham eigenvalues for Hybrid Functionals
Physical Review B, 2010Co-Authors: Thomas Korzdorfer, Stephan KümmelAbstract:The quasiparticle interpretation of Kohn-Sham (KS) and generalized Kohn-Sham (GKS) eigenvalues is a frequently used tool to facilitate the analysis of experimental photoelectron spectra. Interpreting GKS eigenvalues from Hybrid Functionals is particularly popular for systems for which KS eigenvalues from semilocal Functionals do not match experimental ionization potentials well. By calculating both KS and GKS eigenvalues for several organic semiconductor molecules, we demonstrate that the usually good interpretability of eigenvalues from Hybrid Functionals is mostly due to their numerical realization in the GKS scheme and not only due to their partial correction of self-interaction. Our results further illustrate why a stretching of the energy axis of KS spectra frequently but not always yields results that compare well to Hybrid and experimental spectra.
