Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session H5: Exact-Exchange Based DFT Functionals Meet Quasiparticle Energy Calculations: Exciting Prospects for Condensed Systems |
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Sponsoring Units: DCOMP Chair: Patrick Rinke, Fritz Haber Institute Room: Colorado Convention Center Korbel 1A-1B |
Tuesday, March 6, 2007 8:00AM - 8:36AM |
H5.00001: Ab-initio study of the excited state properties of liquid water Invited Speaker: Lucia Reining In the last decades, we have witnessed an increasing interest on water and many studies on the geometry and ground state properties have appeared in the literature. Nevertheless, its excited state properties, which are essential to study the chemical and physical behavior of many biological and industrial processes, have not been investigated yet. We present here ab-initio calculations, in the framework of many body Green's function formalism, of liquid water. We use snapshots taken from classical molecular dynamics as input geometries for the study of the electronic and optical spectra. The excitation spectra are first obtained within the Density Functional Theory (DFT) and then corrected within the ``GW'' approximation. The optical absorption spectra are calculated by solving the Bethe-Salpeter equation; they result modified, with respect to the DFT spectra, suggesting the presence of important excitonic effects at low energies. [Preview Abstract] |
Tuesday, March 6, 2007 8:36AM - 9:12AM |
H5.00002: GW/Bethe-Salpeter Calculations for Solids for Core and Valence Spectra Invited Speaker: Eric L. Shirley The introduction of self-energy corrections to density- functional calculations has greatly improved the one-electron properties of materials. GW calculations are a prime example of this. Excitation spectra, meanwhile, often probe the excited states of materials that involve the excitation of at least one electron across the Fermi level, producing an electron-hole pair. This can be the case for optical absorption and inelastic scattering of x-rays and electrons. Because of interactions in the excited state between the electron and hole, it is preferable to solve the coupled two-particle equation of motion for the electron-hole pair. Bethe-Salpeter-equation (BSE) calculations are a prime example of this. In addition to solving the equation of motion for an interacting electron and hole moving in a static solid, one can try to include lifetime- damping and other effects in the absorption spectrum. In this talk, I would like to present a framework that allows treatment of excitation spectra in a wide variety of materials, ranging from traditional semiconductors and insulators to fairly complicated minerals. This will also facilitate consideration of uniaxial birefringence, spatial-dispersion-induced birefringence, multiplet effects, and electric-quadrupole transitions in x-ray spectra. [Preview Abstract] |
Tuesday, March 6, 2007 9:12AM - 9:48AM |
H5.00003: New hybrid functionals for ab-initio calculations of properties of solids Invited Speaker: Gustavo Scuseria This presentation will address our current efforts to develop more accurate exchange-correlation functionals for Density Functional Theory. The functional to be discussed is a screened Coulomb potential exchange hybrid called \textbf{HSE} [1], which is particularly suited for calculations in solids because it is much faster than regular hybrids and can also be used in metals and systems with negligble band gaps. \textbf{HSE} yields an important improvement in band gap estimates [2] compared to \textbf{LDA}, \textbf{GGAs}, and meta-\textbf{GGAs.} We will also present applications to transition metal oxides, silicon phase transitions and defects [3], and other problems where electron localization seems to play a crucial role [4]. \newline \newline [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, \textit{J. Chem. Phys.} \textbf{118}, 8207 (2003); J. Heyd and G. E. Scuseria, \textit{J. Chem. Phys.} \textbf{120}, 7274 (2004); J. Heyd and G. E. Scuseria, \textit{J. Chem. Phys.} \textbf{121}, 1187 (2005). \newline [2] J. Heyd, J. E. Peralta, G. E. Scuseria, and R. L. Martin, \textit{J. Chem. Phys.} \textbf{128}, 174101 (2005); J. E. Peralta, J. Heyd, G. E. Scuseria, and R. L. Martin, Phys. Rev. \textbf{B 74}, 073101 (2006). \newline [3] E. R. Batista, J. Heyd, R. G. Hennig, B. P. Uberuaga, R. L. Martin, G. E. Scuseria, C. J. Umrigar, and J. W. Wilkins, Phys. Rev. B \textbf{74}, 121102(R) (2006). \newline [4] I. D. Prodan, G. E. Scuseria, and R. L. Martin, Phys. Rev. B \textbf{73}, 045104 (2006). [Preview Abstract] |
Tuesday, March 6, 2007 9:48AM - 10:24AM |
H5.00004: Hybrid functional and selfconsistent GW$\Gamma$ calculations for solids Invited Speaker: Georg Kresse $GW$ calculations in various flavors are presented for small gap and large gap systems, comprising typical semiconductors (Si, SiC, GaAs, GaN, ZnO, ZnS, CdS and AlP), small gap semiconductors (PbS, PbSe, PbTe), insulators (C, BN, MgO, LiF) and noble gas solids (Ar, Ne). The general finding is that single shot $G_0W_0$ calculations based on wavefunctions obtained by conventional density functional theory calculations yield too small band gaps, whereas $G_0W_0$ calculations following hybrid Hartree-Fock density functional calculations tend to overestimate the band gaps by roughly the same amount. This is at first sight astonishing, since the hybrid functionals yield very good band gaps themselves. The contradiction is resolved showing that the inclusion of the attractive electron-hole interactions (excitonic effects) are required to obtain good static and dynamic dielectric functions using hybrid functionals. The corrections are usually incorporated in GW using ``vertex corrections'', and, in fact, inclusion of vertex corrections rectifies the predicted band gaps. In order to remove the dependency on the initial wavefunctions we furthermore present selfconsistent GW calculations, again including an approximate treatment of vertex corrections. The results are in excellent agreement with experiment, with a few percent deviations for all considered materials. We conclude that predictive band gap engineering is now possible with the theoretical description approaching experimental accuracy. Finally the relationship between the $GW$ method and hybrid functionals is use to elaborate on the shortcomings of hybrid functionals for large gap systems and metals. [Preview Abstract] |
Tuesday, March 6, 2007 10:24AM - 11:00AM |
H5.00005: Optimized effective potential methods for molecules and solids Invited Speaker: Andreas Goerling The relation of the optimized effective potential (OEP) method to density-functional theory and in particular to Kohn-Sham (KS) methods is discussed. It is shown that OEP approaches only represent proper KS methods if the basis set for the one-particle functions and the basis set for the effective potential are well balanced. It is shown that exact exchange KS methods based on the OEP approach not only yield band structures that are improved compared to band structures resulting from conventional KS approaches but that exact exchange magnetization-current density-functional theory implemented via an OEP approach represents a framework for a unified treatment of magnetic effects, spin-orbit interactions, and magnetization currents. [Preview Abstract] |
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