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During the last decade, quasiparticle calculations have been used successfully to describe the electronic excited-state properties of solids such as single-particle band structures and absorption spectra. The Coulomb interaction between N electrons correlates their motion. As a consequence, an exact description of the N-electron problem requires the solution of an equation with 3N coupled spatial degrees of freedom. For macroscopic systems, the number of electrons N is on the order of Avogadro's number (about 10²³), so a solution to the N-electron problem must be approximate.

A successful approximation for the determination of excited states is based on the quasiparticle concept and the Green function method. The Coulomb repulsion between electrons leads to a depletion of negative charge around a given electron and the ensemble of this electron and its surrounding positive screening charge forms a quasiparticle. The mathematical description of quasiparticles is based on the single-particle Green function G, whose exact determination requires complete knowledge of the quasiparticle self-energy. The self-energy is a non-Hermitian, energy-dependent, and non-local operator that describes exchange and correlation effects beyond the Hartree approximation.

A determination of the self-energy can only be approximate, and a working scheme for the quantitative calculation of excitation energies in metals, semiconductors, and insulators is the so-called dynamically screened interaction or the GW approximation (GWA). In this approximation, the self-energy is the product of the single-particle Green function G and the screened interaction W. The GWA for the computation of quasiparticle energies was proposed by Hedin in 1965. However, not until the mid-eighties was the approach applied to large-scale, numerical electronic structure calculations. The resulting ab-initio band structures compare favorably with experiment and are reviewed here.

Talk on ``Review of Quasiparticle Calculations''

Review of Quasiparticle Calculations (1.3 MB) (to be published in Solid State Physics 54, 1 (1999)).
Download file as review.uu and type ``csh review.uu'' to obtain postscript file.

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Materials Science: Review of Quasiparticle Calculations
<http://www.physics.ohio-state.edu/~aulbur/gw/review.html>