Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 99: Electronic structure theory

HL 99.3: Vortrag

Donnerstag, 3. April 2014, 15:30–15:45, POT 151

Eigenvalues from Density Functional Theory with exact exchange – chances and limitations — •Tobias Schmidt and Stephan Kümmel — University of Bayreuth, Germany

Density Functional Theory (DFT) has become one of the most widely used methods for electronic structure calculations, e.g., for predicting molecular geometries and binding energies. Also DFT eigenvalues are often used for physical predictions, e.g., for band structure studies. However, while functionals such as the Generalized Gradient Approximations can predict electronic binding reasonably, their limitations in band structure prediction are well known. On the other hand it has been reported that exact Kohn-Sham exchange (EXX) yields reasonable band structures, but its binding energy predictions are poor.

We here report a detailed investigation of so called Local Hybrid Functionals (LHFs), which strive to combine full, non-local Fock-exchange with a non-local, compatible correlation functional. We demonstrate that this functional class allows for an improved description of binding properties and an enhanced interpretability of the eigenvalues. However, we also point out that all presently available functionals that incorporate EXX lead to a fundamental imbalance between their accuracy for eigenvalues and for binding energies.

To shed light on this issue we analyze the local multiplicative potential from LHFs, finding that it does not reach the correct form in the limit |r|→ ∞. The potential is affected by the occurrence of nodal planes in the highest occupied KS orbital, and counterintuitively approaches different limits in different directions of space.

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