Diabatic electronic states from many-body perturbation theory.

We apply the so-called diabatization method by Baer (1975 Chem. Phys. Lett. 35 112) to describe photo-excited electronic states. The diabatization is a unitary transformation which, applied to the adiabatic eigenstates of the quantum Hamiltonian, allows for treating the non-adiabatic effects correctly. These effects are all those which appear in the Born-Oppenheimer approximation as the areas of avoided crossings in the potential energy surfaces. The diabatization is placed in the context of the scheme of ab initio many-body perturbation theory (density functional theory with the GW method with Bethe-Salpeter equation (DFT-GW-BSE)) calculation of materials. [ABSTRACT FROM AUTHOR]