Berlin 2008 – scientific programme

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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 1.5: Invited Talk

Thursday, February 28, 2008, 11:30–12:00, A 151

The Quasiparticle Self-Consistent GW Approximation — •Mark van Schilfgaarde — Arizona State University, Tempe AZ

In many-body perturbation theory, the self-energy Σ is constructed in a perturbation expansion in some noninteracting quasiparticles, generated by a noninteracting hamiltonian H₀ or Green’s function G₀. The perturbation theory generates an interacting Green’s function G. We introduce the idea of a self-consistent perturbation, where G₀ is chosen to be as close as possible to G, to minimize the size of the perturbation. We have implemented the idea in the GW approximation, which we call the quasiparticle self-consistent GW (QSGW) approximation. QSGW handles both itinerant and correlated electrons on an equal footing, in a true ab initio manner. It describes optical properties in a wide range of materials rather well, including cases where the local-density and LDA-based GW approximations fail qualitatively. Self-consistency dramatically improves agreement with experiment, and is sometimes essential. Weakly correlated materials such as Na, and sp semiconductors are described with uniformly high accuracy. QSGW reliably treats many aspects of correlated materials. Spin wave spectra in Fe, MnO, NiO and MnAs are uniformly well described.

QSGW avoids some formal and practical problems encountered in the LDA-based and self-consistent GW, which will be discussed. Discrepancies with experiments are highly systematic and increase with localization of the eigenfunctions. We will present results for several materials classes to illustrate this, and offer arguments to show what extra diagrams must be included to account for the discrepancies.