Optical band gaps from experiment, compared with the noninterpolated photoemission gaps calculated using the scGW method, and the optical gaps calculated using scGW-RPA and scGW-BSE

We pubblised a new paper¹ on the optical properties of Cu-chalcogenide photovoltaic absorbers. In this manuscript we  calculate the optical response of the less studied, but promising, Cu₂ZnGe(S,Se)₄ compounds, opening the way to predictive calculations of still unknown materials by means of self-consistent GW plus Bethe-Salpeter equations.
Moreover in this paper we solved the problem of the dipoles calculation starting from self-consistent GW or in general from any non-local self-energy/functional. We used the dipoles definition of Blount²
and finite difference approach to define dipoles without calculate any commutator with the non-local part of the Hamiltonian.
References:

1. Optical properties of Cu-chalcogenide photovoltaic absorbers from self-consistent GW and the Bethe-Salpeter equation
   Phys. Rev. B 91, 075134 (2015)
   Sabine Körbel, David Kammerlander, Rafael Sarmiento-Pérez, Claudio Attaccalite, Miguel A. L. Marques, and Silvana Botti
    
2. Formalisms of band theory
   E.I. Blount, Solid State Physics, 13, page 305-73. New York, Academic Press, (1962)