An excitation matched local correlation approach to excited state specific perturbation theory

TL;DR

This paper introduces a cubic-scaling, excited-state-specific perturbation theory method that maintains accuracy by matching local correlation treatments between states, effectively handling charge transfer excitations.

Contribution

It presents a novel local correlation approach with cubic scaling for excited states, accurately matching ground and excited state correlation energies.

Findings

Achieves cubic scaling for excited-state calculations.

More accurate than EOM-CCSD for charge transfer states.

Reproduces CC3 excitation energies within 0.1 eV.

Abstract

We develop a cubic scaling approach to excited-state-specific second order perturbation theory in which the completeness of a local correlation treatment is carefully matched between the ground and excited state. With this matching, the accuracy of the parent method is maintained even as substantial portions of the correlation energy are neglected. Even when treating a long-range charge transfer excitation, cubic scaling is achieved in systems with as few as ten non-hydrogen atoms. In a test on the influence of an explicit solvent molecule on a long range charge transfer, the approach is qualitatively more accurate than EOM-CCSD and reproduces CC3's excitation energies and excited state potential energy surface to within about 0.1 eV and 0.5 kcal/mol, respectively.