Range-separated time-dependent density-functional theory with a frequency-dependent second-order Bethe-Salpeter correlation kernel

TL;DR

This paper introduces a range-separated TDDFT method combining short-range DFT and long-range Bethe-Salpeter kernels to improve electronic excitation energy calculations, moving beyond the adiabatic approximation.

Contribution

It develops a novel range-separated TDDFT approach with a frequency-dependent second-order Bethe-Salpeter kernel, enhancing excitation energy accuracy.

Findings

Slight improvement in excitation energies for small molecules.

Method effectively combines DFT and Green's function approaches.

Preliminary results show promising accuracy enhancements.

Abstract

We present a range-separated linear-response time-dependent density-functional theory (TDDFT) which combines a density-functional approximation for the short-range response kernel and a frequency-dependent second-order Bethe-Salpeter approximation for the long-range response kernel. This approach goes beyond the adiabatic approximation usually used in linear-response TDDFT and aims at improving the accuracy of calculations of electronic excitation energies of molecular systems. A detailed derivation of the frequency-dependent second-order Bethe-Salpeter correlation kernel is given using many-body Green-function theory. Preliminary tests of this range-separated TDDFT method are presented for the calculation of excitation energies of the He and Be atoms and small molecules (H2, N2, CO2, H2CO, and C2H4). The results suggest that the addition of the long-range second-order Bethe-Salpeter correlation kernel overall slightly improves the excitation energies.