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O: Fachverband Oberflächenphysik

O 42: Focus Session: Frontiers of Electronic-Structure Theory – Advances in Time-Dependent and Nonequilibrium Ab Initio Methods III

O 42.8: Talk

Wednesday, March 20, 2024, 12:15–12:30, HE 101

Beyond the GW approximation using effective interactions — •Abdallah El Sahili — École Polytechnique

Electron addition and removal spectra as well as the total ground state energy can be expressed in terms of the one-body Green*s function. Often, the Dyson equation with an approximate self-energy is solved to access this quantity. Today, the probably most widely used approximation is Hedin's GW self-energy [1], which has become the state-of-the-art for the band structure calculations of solids. However, GW still suffers from the existence of a variety of different flavors that lead to a sometimes significant spread of results, it has problems to describe satellite structures in the spectral function, and it is limited to a range of materials where correlations are weak to moderate. Especially total energy calculations present a number of open questions. In the present work we concentrate on the screened interaction W. On one side, we discuss the different perturbation expansions for the self-energy that can be explored according to the choice of W. On the other side, we generalize the concept of the screened interaction to a generalized effective interaction, for which we derive in principle exact equations as well as promising approximations. We show that this allows one to go beyond the GW approximation in an efficient way, avoiding the computational complexity of full vertex corrections. Illustrations for the general findings are given using the half-filled symmetric Hubbard dimer.

[1] Lars Hedin, Phys. Rev. 139, A796 (1965)

Keywords: Green's function; Beyond GW; Total energy; Effective interactions; Self-energy