Ab initio many-body treatment of the electronic structure of metals

Abstract

We propose and apply a combination of an a.b initio (band-structure) calculation with to many[)oily' treatment, including screening- effects. We start from a linearized muffin-tin orbital (LMTO) calculation to determine the Bloch functions or the Hartree one-particle Hamiltonian, from which we calculate the static susceptibility and dielectric function within the standard random phase approximation (RPA). Freon the Bloch functions we obtain maximally localized Wannier functions, using a method proposed by Marzari and Vanderbilt. Within this Wannier basis all relevant one-particle and unscreened and screened Coulomb matrix elements are calculated. This yields a multi-band Hamiltonian in second quantization with ab initio parameters, for which screening has been taken into account within the simplest. standard approximation. Then, established methods of many-body theory are used. We apply this concept to a simple metal, namely lithium (Li). Here the maximally localized Wannier functions turn out. to be of the sp 3 -orbital kind. Furthermore, only the on-site contributions of the screened Coulomb matrix elements are relevant, and a. generalized, four-band Hnbbard model is justified. The screened on-site Coulomb matrix elements are considerably smaller than the band width because of which it, is sufficient to calculate the selfenergv in weak-coupling approximation. We compare results obtained within the screened Jartree-Fock approximation (HFA) and within the second-order perturbation theory (SOPT) in the Coulomb matrix elements for Li and find that many-body effects are small but not negligible even for this simple metal.