Charge-transfer in time-dependent density-functional theory via spin-symmetry-breaking

TL;DR

This paper demonstrates that spin-symmetry-breaking in time-dependent density functional theory provides an effective and simple approach to accurately model long-range charge-transfer excitations, especially in molecules with open-shell fragments.

Contribution

The study introduces spin-symmetry-breaking as a novel solution for improving charge-transfer excitation predictions in TDDFT for open-shell systems.

Findings

Spin-symmetry-breaking yields accurate charge-transfer excitations at large separations.

Unrestricted exact-exchange functionals improve excitation energy predictions.

Results are validated on 1D models and the LiH molecule.

Abstract

Long-range charge-transfer excitations pose a major challenge for time-dependent density functional approximations. We show that spin-symmetry-breaking offers a simple solution for molecules composed of open-shell fragments, yielding accurate excitations at large separations when the acceptor effectively contains one active electron. Unrestricted exact-exchange and self-interaction-corrected functionals are performed on one-dimensional models and the real LiH molecule within the pseudopotential approximation to demonstrate our results.