Calculation of correlation functions for interacting quasiparticles in crystals

J. W. Halleý

H. V. Grushevskaya, Л. И. Гурский

Variation principle has been developed to calculate many-particle effects in crystals. Within the framework of quasi-particle concept the variation principle has been used to find one-electron states with taking into account of effects due to non-locality of electronic density functional in electromagnetic fields. A secondary quantized density matrix was used to find the Green function of a quasiparticle and changes of its effective mass due to correlated motion of interacting electrons.

A. L. Kuzemsky

The self-consistent theory of the correlation effects in Highly Correlated Systems(HCS) is presented. The novel Irreducible Green's Functions(IGF) method is discused in detail for the Hubbard model and random Hubbard model. The interpolative solution for the quasiparticle spectrum, which is valid for both the atomic and band limit is obtained. The (IGF) method permits to calculate the quasiparticle spectra of many-particle systems with the complicated spectra and strong interaction in a very natural and compact way. The inelastic scattering corrections leads to the damping of the quasiparticles and are the main topic of the present consideration. The calculation of the damping has been done in a self-consistent way for both limits. For the random Hubbard model the weak coupling case has been considered and the self-energy operator has been calculated using the combination of the IGF method and Coherent Potential Approximation (CPA). The other applications of the method to s-f model, Anderson model, Heisenberg antiferromagnet, electron-phonon interaction models are discussed briefly.

Julia Wildeboer

Günther Engel, Behnam Farid, C.M.M. Nex +1 more

The concepts of quasiparticle and collective excitation are considered in the context of continued-fraction expansions. This leads to a practical scheme allowing a highly accurate description of the screened interaction function W and the electron self-energy \ensuremath{\Sigma}, which can be achieved at a reasonable computational cost. The usefulness of this scheme is demonstrated on a simple two-band model of a semiconductor, where it leads to an unambiguous calculation of the electron self-energy in the GW approximation. Conceptually, the theory clarifies some of the limitations of the standard quasiparticle concept in many-body theory. Furthermore, it allows a proper assessment of the quality of the standard approximations employed in GW calculations.