Regensburg 2007 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 26: Electronic properties III

MM 26.1: Vortrag

Mittwoch, 28. März 2007, 16:45–17:00, H6

Density matrix functional theory versus density functional theory: application to the Hubbard model — •Ryan Requist and Oleg Pankratov — Lst. für Theoretische Festkörperphysik, Universität Erlangen-Nürnberg

While the Hohenberg-Kohn theorem was long ago extended to prove a one-to-one correspondence between the first order reduced density matrix (RDM) and a nonlocal external potential [1], only recently have approximate RDM functionals been applied to systems such as atoms, small molecules, and the homogeneous electron gas. We study a two site Hubbard model which is exactly solvable; therefore, it provides a context for an explicit comparison of the density functional (DFT) and RDM functional approaches. In the RDM formalism, the Kohn-Sham (KS) system generally has fractionally occupied states, and all of these are degenerate, which is quite different from the common KS-DFT approach. The iteration of the self-consistent RDM equations leads to a nonlinear discrete map. Due to the degeneracy of the KS spectrum of the ground state RDM, an analogue of the Jahn-Teller theorem implies that the ground state is an unstable fixed point of the iteration map. The RDM energy functional constructed here may be useful for studying strongly correlated systems.

[1] T. L. Gilbert, Phys. Rev. B 12, 2111 (1975).