Berücksichtigung von Abschirmungs- und Wechselwirkungseffekten in Ab-Initio-Berechnungen der elektronischen Struktur von Festkörpern

For the determination of the electronic structure of solids we propose and apply a combination of an ab initio calculation with a many-body treatment including screening effects. We determine a Hamiltonian in second quantisation with ab-initio calculated parameters. For this Hamiltonian methods of many-body theory are applied. At first we perform a simple Hartree-Fock calculation. This yields one-particle results, which can be compared to the bandstructures from a DFT LDA calculation. To include screening effects, we calculate statically screened Coulomb matrix elements, and use these matrix elements for the Fock term, as a static $GWA$ calculation. We apply this concept to the simple metal Lithium (Li). Here a weak coupling treatment within the second order perturbation theory is justified. As a result, for Li many body effects are small but not negligable. The resulting density of states in SOPT turns out to be shifted and smeared out by the finite imaginary part of self energy.