Berlin 2008 – wissenschaftliches Programm

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SYEC: Symposium Exact-exchange and hybrid functionals meet quasiparticle energy calculations

SYEC 1: Exact-exchange and hybrid functionals meet quasiparticle energy calculations I

SYEC 1.3: Hauptvortrag

Donnerstag, 28. Februar 2008, 10:30–11:00, A 151

GW and hybrid functionals applied to extended systems — •Georg Kresse — Faculty of Physics, University of Vienna

GW calculations are presented for small gap and large gap systems, comprising typical semiconductors (Si, SiC, GaAs, GaN, ZnO, ZnS, CdS and AlP), insulators (C, BN, MgO, LiF) and noble gas solids (Ar, Ne). The general finding is that single shot G0W0 calculations using wavefunctions obtained by conventional density functional theory calculations yield too small band gaps, whereas G0W0 calculations following hybrid Hartree-Fock density functional calculations tend to overestimate the band gaps. This is at first sight astonishing, since hybrid functionals themselves yield very good band gaps. The contradiction is resolved by showing that the a proper treatment of the attractive electron-hole interaction (excitonic effects) is required to obtain good static and dynamic dielectric functions using hybrid functionals. The corrections are incorporated in GW using vertex corrections, and the inclusion of these vertex corrections rectifies the predicted band gaps.

In order to remove the dependency on the initial wavefunctions, selfconsistent GW calculations are presented, again including a many body treatment of vertex corrections. The results are in excellent agreement with experiment, with a few percent deviations for all considered materials. Finally an outlook on total energy calculations based on GW methods is given and the shortcommings of hybrid functionals are discussed in this light.