Combining linear interpolation with extrapolation methods in rangeseparated ensemble density functional theory
Abstract
The combination of a recently proposed linear interpolation method (LIM), which enables the calculation of weightindependent excitation energies in rangeseparated ensemble density functional approximations, with the extrapolation scheme of Savin is presented in this work. It is shown that LIM excitation energies vary quadratically with the inverse of the rangeseparation parameter μ when the latter is large. As a result, the extrapolation scheme, which is usually applied to longrange interacting energies, can be adapted straightforwardly to LIM. This extrapolated LIM (ELIM) has been tested on a small test set consisting of He, Be, H_{2} and HeH^{+}. Relatively accurate results have been obtained for the first singlet excitation energies with the typical μ = 0.4 value. The improvement of LIM after extrapolation is remarkable, in particular for the doubly excited 2^{1}Σ^{+}_{g} state in the stretched H_{2} molecule. Threestate ensemble calculations in H_{2} also show that ELIM does not necessarily improves relative excitation energies, even though individual excitation energies are more accurate after extrapolation. Finally, an alternative decomposition of the shortrange ensemble exchangecorrelation energy is proposed in order to correct for ghostinteraction errors in multideterminant rangeseparated ensemble density functional theory calculations. The implementation and calibration of such a scheme are currently in progress.
 Publication:

Molecular Physics
 Pub Date:
 April 2016
 DOI:
 10.1080/00268976.2015.1119902
 arXiv:
 arXiv:1509.08033
 Bibcode:
 2016MolPh.114..968S
 Keywords:

 Ensemble density functional theory;
 range separation;
 linear interpolation method;
 ghost interaction;
 Physics  Chemical Physics
 EPrint:
 25 pages, 7 figures