Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 37: Posters: Plasmonics, Electronic Structure and Spin-Orbit Interaction, Semiconductor and Insulator Surfaces, Nanostructures

O 37.46: Poster

Tuesday, April 1, 2014, 18:30–22:00, P2

Solution of the GW-based quasiparticle-equation beyond the diagonal approximation: improvements in energies and wavefunctions — •Ferdinand Kaplan¹, Michiel van Setten², and Ferdinand Evers¹ — ¹Karlsruhe Institute of Technology — ²Université catholique de Louvain

One of the most used approaches for the computational study of solids, nanoscale systems and molecules is the density functional theory (DFT). However, as is well known, DFT calculations of single particle excitation spectra, e.g. ionization potentials, often suffer from approximations in exchange correlations potentials. To systematically improve the estimation of quasi-particle energies for molecular system, we have implemented the so called GW method into a standard quantum chemistry package (G₀W₀-level). The approach represents a perturbative expansion of the many-body Green’s function with respect to the screened interaction, W.

A central mathematical step in GW is the solution of the quasiparticle (qp-) equation. It finds the poles of the (approximate) many-body Greens function, that define the qp-energies. A common simplification in this procedure is to neglect all off-diagonal elements of the self-energy matrix, that enters the qp-equation. We investigate the quantitative error associated with this approximation for a typical set of molecules and find significant effects. Including the off-diagonal terms the ionization potential experiences shifts (usually towards less binding) reaching 100mV or more.