A well-tempered density functional theory of electrons in molecules

TL;DR

This paper extends a density functional theory approach with correct long-range behavior, introducing practical methods for parameter determination and demonstrating its effectiveness in predicting various molecular properties.

Contribution

It introduces a semi-empirical functional with optimized parameters for better accuracy in molecular property predictions.

Findings

Good reproduction of ionization potentials

Accurate description of valence, Rydberg, and charge-transfer excitations

Broad applicability to static and dynamic molecular properties

Abstract

Reporting extensions of a recently developed approach to density functional theory with correct long-range be-havior (Phys. Rev. Lett. 94, 043002 (2005)). The central quantities are a splitting functional gamma[n] and a complementary exchange-correlation functional. We give a practical method for determining the value of \gamma in molecules, assuming an approximation for XC energy is given. The resulting theory shows good ability to reproduce the ionization potentials for various molecules. However it is not of sufficient accuracy for forming a satisfactory framework for studying molecular properties. A somewhat different approach is then adopted, which depends on a density-independent \gamma and an additional parameter w eliminating part of the local exchange functional. The values of these two parameters are obtained by best-fitting to experimental atomization energies and bond-lengths of the molecules in the G2(1) database. The optimized values are gamma=0.5 a_0^{-1} and w=0.1 . We then examine the performance of this slightly semi-empirical functional for a variety of molecular properties, comparing to related works and to experiment. We show that this approach can be used for describing in a satisfactory manner a broad range of molecular properties, be they static or dynamic. Most satisfactory is the ability to describe valence, Rydberg and inter-molecular charge-transfer excitations.