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TT: Fachverband Tiefe Temperaturen

TT 5: Correlated Electrons - (General) Theory

TT 5.6: Vortrag

Montag, 26. März 2007, 15:30–15:45, H18

Ab-initio wavefunction-based methods for solids: correlation corrections to the band structure of oxide compounds — •Liviu Hozoi, Uwe Birkenheuer, and Peter Fulde — Max-Planck-Institut fuer Physik komplexer Systeme, 01187 Dresden

We apply ab-initio wavefunction-based methods to the study of correlation effects on the band structure of oxide compounds. We choose MgO as a prototype closed-shell system. As a zeroth-order approximation, we compute first the Hartree-Fock (HF) bands and the (localized) Wannier orbitals associated with these. The HF data for the infinite crystal is transferred then to a quantum chemical program and used as input for the construction of embedded clusters. Correlation effects on the fundamental band gap and on band widths are computed by using a quasiparticle picture and a local Hamiltonian approach. For the (N-1)/(N+1) valence and conduction band states, we found that relaxation and polarization effects associated with the on-site and nearest-neighbor ligand electron shells account for 40% of the difference between the HF and experimental gaps. Long-range polarization effects bring also large corrections. Within the approximation of a dielectric continuum, these corrections amount to 50% of the difference between the HF and experimental gap values. Whereas correlation effects are important for estimating band gaps, we found that they produce only minor changes on the HF band widths, at least in this material. The results show that our approach, based on a transparent formalism and well-controlled approximations, is able to provide a good understanding of the major effects that determine the electronic band structure.