Alternative separation of exchange and correlation energies in range-separated density-functional perturbation theory

TL;DR

This paper introduces an alternative way to separate exchange and correlation energies in range-separated density-functional perturbation theory, leading to improved accuracy in modeling noble-gas dimers.

Contribution

It proposes a novel energy separation method using a long-range interacting wavefunction, resulting in a range-separated double-hybrid functional that captures long- and short-range correlation coupling.

Findings

Improved potential energy curves for noble-gas dimers.

Enhanced accuracy of binding energies and bond distances.

Demonstrates significance of long- and short-range correlation coupling.

Abstract

An alternative separation of short-range exchange and correlation energies is used in the framework of second-order range-separated density-functional perturbation theory. This alternative separation was initially proposed by Toulouse et al. [Theor. Chem. Acc. 114, 305 (2005)] and relies on a long-range interacting wavefunction instead of the non-interacting Kohn-Sham one. When second-order corrections to the density are neglected, the energy expression reduces to a range-separated double-hybrid (RSDH) type of functional, RSDHf, where "f" stands for "full-range integrals" as the regular full-range interaction appears explicitly in the energy expression when expanded in perturbation theory. In contrast to usual RSDH functionals, RSDHf describes the coupling between long- and short-range correlations as an orbital-dependent contribution. Calculations on the first four noble-gas dimers show that this coupling has a significant effect on the potential energy curves in the equilibrium region, improving the accuracy of binding energies and equilibrium bond distances when second-order perturbation theory is appropriate.