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O: Fachverband Oberflächenphysik

O 48: Focussed session: Theory and computation of electronic structure: new frontiers IV (jointly with HL, DS)

O 48.7: Vortrag

Mittwoch, 16. März 2011, 16:45–17:00, TRE Phy

Accurate and efficient density-functional calculations for the electronic entropy — •Rudolf Zeller — Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich

The calculation of the electronic entropy S(T) as function of temperature is a numerically demanding problem for metallic systems because S(T) depends logarithmically on the Fermi-Dirac distribution which varies rapidly near the Fermi level. Therefore, very accurate Brillouin zone samplings are usually needed.

I will present a technique based on complex energy contour integration and show how significant reduction of the number of sampling points can be achieved and how the problem of undetermined phases of complex valued logarithms can be avoided. The technique exploits the analytical properties of the Green function of the single-particle Kohn-Sham equation and has been implemented within the full-potential Korringa-Kohn-Rostoker method, where the use of Lloyd's formula guarantees fast convergence with respect to the angular momentum cutoff.

As a by-product I obtain a broadening scheme for total energy calculations with error elimination up to the sixth power of T. I will also explain particular advantages of Fermi-Dirac broadening (besides its direct physical significance) compared to other broadening schemes.