Assessment of range-separated time-dependent density-functional theory for calculating C6 dispersion coefficients

TL;DR

This study evaluates a range-separated TDDFT approach combining long-range HF exchange with short-range LDA to calculate C6 dispersion coefficients, showing modest improvements over standard TDDFT and close to TDHF accuracy.

Contribution

The paper introduces and assesses a range-separated TDDFT method that improves C6 coefficient predictions by incorporating long-range HF exchange with LDA kernels.

Findings

Range-separated TDDFT slightly improves C6 accuracy over standard TDDFT.

The method achieves errors close to time-dependent Hartree-Fock.

Long-range HF exchange has a beneficial impact on dispersion coefficient calculations.

Abstract

We assess a variant of linear-response range-separated time-dependent density-functional theory (TDDFT), combining a long-range Hartree-Fock (HF) exchange kernel with a short-range adiabatic exchange-correlation kernel in the local-density approximation (LDA) for calculating isotropic C6 dispersion coefficients of homodimers of a number of closed-shell atoms and small molecules. This range-separated TDDFT tends to give underestimated C6 coefficients of small molecules with a mean absolute percentage error of about 5%, a slight improvement over standard TDDFT in the adiabatic LDA which tends to overestimate them with a mean absolute percentage error of 8%, but close to time-dependent Hartree-Fock which has a mean absolute percentage error of about 6%. These results thus show that introduction of long-range HF exchange in TDDFT has a small but beneficial impact on the values of C6 coefficients. It also confirms that the present variant of range-separated TDDFT is a reasonably accurate method even using only a LDA-type density functional and without adding an explicit treatment of long-range correlation.