Short-range Functionals Research Articles

Properties of short-range and long-range correlation energy density functionals from electron-electron coalescence

The combination of density functional theory with other approaches to the many-electron problem through the separation of the electron-electron interaction into a short-range and a long-range contribution is a promising method, which is raising more and more interest in recent years. In this work some properties of the corresponding correlation energy functionals are derived by studying the electron-electron coalescence condition for a modified (long-range-only) interaction. A general relation for the on-top (zero electron-electron distance) pair density is derived, and its usefulness is discussed with some examples. For the special case of the uniform electron gas, a simple parameterization of the on-top pair density for a long-range only interaction is presented and supported by calculations within the ``extended Overhauser model''. The results of this work can be used to build self-interaction corrected short-range correlation energy functionals.

Local density approximation for long-range or for short-range energy functionals?

Density functional methods were developed, in which the Coulomb electron–electron interaction is split into a long- and a short-range part. In such methods, one term is calculated using traditional density functional approximations, like the local density approximation. The present paper tries to shed some light upon the best way to do it by comparing the accuracy of the local density approximation with accurate results for the He atom.

A short-range gradient-corrected density functional in long-range coupled-cluster calculations for rare gas dimers

A previously proposed scheme for coupling short-range (sr) density functionals with wavefunction-based long-range (lr) ab initio methods has been extended by (a) developing a new gradient-corrected sr functional of the Perdew-Burke-Ernzerhof (PBE) type and (b) introducing coupled-cluster (CC) approaches (CC with single and double excitations (CCSD), and with additional perturbative triples (CCSD(T))) at the ab initio side. The results show that mixing-in of lr-ab initio correlation helps to remove deficiencies of currently used density functionals for the treatment of van-der-Waals interactions. Compared to full ab initio calculations, the basis set dependence is weaker so that the accuracy of the mixed results surpasses that of the ab initio ones for basis sets of triple-zeta quality.

Short-range exchange and correlation energy density functionals: Beyond the local-density approximation

We propose approximations which go beyond the local-density approximation for the short-range exchange and correlation density functionals appearing in a multideterminantal extension of the Kohn-Sham scheme. A first approximation consists of defining locally the range of the interaction in the correlation functional. Another approximation, more conventional, is based on a gradient expansion of the short-range exchange-correlation functional. Finally, we also test a short-range generalized-gradient approximation by extending the Perdew-Burke-Ernzerhof exchange-correlation functional to short-range interactions.

Combining long-range configuration interaction with short-range density functionals

A density functional for short-range electron-electron interaction recently developed by one of us, has been implemented into a multi-reference configuration-interaction code with explicit treatment of long-range interaction only. Possible advantages of such an approach are discussed, using as examples some closed-shell atoms (Be, Ne) and diatomics (H 2, Li 2, C 2, N 2, F 2).