Impact of widely used approximations to the G 0W 0 method: An all-electron perspective

Abstract

Focusing on the fundamental band gaps in Si, diamond, BN, LiF, AlP, NaCl, CaSe and GaAs, and the semicore d-state binding energies in ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe and GaN, we study the differences between the all-electron (AE) and the pseudopotential (PP)-based G 0W 0 method. Leaving aside issues related to the choice of PPs within PP-G 0W 0, we analyze in detail the well-known discrepancies between AE-G 0W 0 and PP-G 0W 0 band gaps by separately addressing the approximations underlying PP-G 0W 0, i.e. the frozen-core approximation, the core-valence partitioning and the use of pseudo-wavefunctions. The largest differences, of the order of eV, appear in the exchange part of the self-energy and the exchange-correlation potential due to the core-valence partitioning. These differences cancel each other and, in doing so, make the final core-valence partitioning effect on the band gaps controllable when the semicore states are treated as valence states. This cancelation, however, is incomplete for semicore d-state binding energies, due to the strong interaction between these semicore states and the deep core. From our comprehensive analysis, we conclude that reliably describing the many-body interactions at the G 0W 0 level and providing benchmark results require an AE treatment. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.