Renormalized Singles Green’s Function for Quasi-Particle Calculations beyond the <i>G</i>₀<i>W</i>₀ Approximation

Abstract

Quasi-particle energies and band gaps in particular are critical for investigating novel materials. Commonly used density functional approximations (DFAs) systematically underestimate band gaps, and GW approximation is the established method of choice for good accuracy and reliability. However, G₀ W₀ has some undesired dependence on the DFA, while self-consistent GW (sc GW) is expensive and not consistent in accuracy improvement. Here a simple and efficient G_RS W₀ approach has been developed: a subspace diagonalization of the Hartree-Fock (HF) Hamiltonian with the DFA density matrix provides the new reference Green's function G_RS that incorporates the effect of all single excitation contributions to the self-energy, thereby essentially eliminating the starting-point dependence. Calculations for molecules and large band gap solids demonstrate the significant improvement over G₀ W₀ and greatly reduced dependence on the initial DFA. G_RS W₀ approach also improve results for other bulks over G₀ W₀, but to a lesser extent, which could be due to the limitations in current implementation for bulks. The results demonstrate that to achieve good accuracy, it is not necessary to use hybrid DFA, which is expensive for bulks. This work should be greatly significant in making GW a more robust approach.