Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 67: Electronic Structure Theory: General, Method Development

O 67.6: Poster

Mittwoch, 18. März 2015, 18:15–21:00, Poster A

RPA spectra from a combination of tetrahedron method and Wannier interpolation — •Johannes Kirchmair, Christoph Friedrich, and Stefan Blügel — Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany

The polarization function within the random-phase approximation (RPA) describes the response of the electron density due to perturbations of the effective potential and is one of the key quantities in many-body perturbation theory. For example, it is employed in the calculations of GW quasiparticle energies, the RPA correlation energy, the Hubbard U parameter, but also in phonon calculations. Very often, practical calculations of the polarization function suffer from severe convergence problems. The convergence with respect to unoccupied states has recently been discussed a lot in literature and correction schemes have been proposed. Another problem is the summation over, in principle, infinitely many k points. The standard method, the so-called tetrahedron method, uses a geometrical interpolation in the three dimensions of reciprocal space that can be understood as the analog of linear interpolation in one dimension. This fast and reliable method, however, shows slow convergence of the spectral properties especially for small frequencies. In this work, we propose to take these low-energy virtual excitations from a Wannier-interpolated band structure. The Wannier interpolation is seamlessly combined with the tetrahedron method, which then takes care of the high-energy virtual excitations. We show test calculations and first results for RPA spectra.