Koopmans spectral functionals in periodic-boundary conditions

Abstract

Koopmans spectral functionals aim to describe simultaneously ground state properties and charged excitations of atoms, molecules, nanostructures and periodic crystals. This is achieved by augmenting standard density functionals with simple but physically motivated orbital-density-dependent corrections. These corrections act on a set of localized orbitals that, in periodic systems, resemble maximally localized Wannier functions. At variance with the original, direct supercell implementation [Phys. Rev. X 8, 021051 (2018)], we discuss here i) the complex but efficient formalism required for a periodic-boundary code using explicit Brillouin zone sampling, and ii) the calculation of the screened Koopmans corrections with density-functional perturbation theory.

Bloch's theorem in orbital-density-dependent functionals: Band structures from Koopmans spectral functionals

“…As an aside, the Wannier-like nature of the orbitals and the Bloch compliance of KC functionals also makes it possible to develop a primitive cell implementation of KC functionals for direct access to the band structure without the need of supercell calculations and of an unfolding procedure; details about the implementation and the results are reported in Ref. [65]. As we already mentioned above, the assumption of having Wannier-like variational orbitals is justified by the observation that the minimization of KC and PZ functionals in extended systems leads to orbitals with these properties.…”