Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 55: Theoretical methods II

O 55.5: Talk

Wednesday, March 28, 2012, 17:45–18:00, MA 043

xcitons in solids captured with bootstrap approximation for the exchange-correlation kernel of time-dependent density functional theory — •Sangeeta Sharma, J. K. Dewhurst, A. Sanna, and E. K. U. Gross — Max-Planck-Institut fur Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany

The ab-initio calculation of optical absorption spectra of nano-structures and solids is a formidable task. The current state-of-the-art is based on many-body perturbation theory: one solves the Bethe-Salpeter equation (BSE). Unfortunately, solving the BSE involves diagonalizing a large matrix making this method computationally very expensive.

Time-dependent density functional theory (TDDFT) is another method able to determine neutral excitations of a system. Although formally exact, the predictions of TDDFT are only as good as the approximation of the exchange-correlation (xc) kernel. There are only a few xc-kernels which correctly reproduce the excitonic effect, but these kernels suffer from either being computationally as expensive as solving BSE or depend upon external parameters.

In our latest work we propose a new approximation[1] for xc-kernel, and demonstrate that this kernel is nearly as accurate as BSE and has the correct 1/q² behavior. The computation cost for the bootstrap kernel is minimal and no system-dependent external parameter is required.

1. S. Sharma, J. K. Dewhurst, A. Sanna, E. K. U. Gross, Phys. Rev. Lett., 107, 186401 (2011).