Transition-Potential Coupled Cluster

TL;DR

This paper introduces the transition-potential coupled cluster (TP-CC) methods, which explicitly treat orbital relaxation in core-hole spectroscopies, significantly improving accuracy without increasing computational cost.

Contribution

The paper proposes a novel TP-CC approach that effectively addresses orbital relaxation errors in core-hole spectra calculations, matching EOM-CCSD accuracy at similar computational cost.

Findings

TP-CCSD(1/2) eliminates orbital relaxation errors

Achieves EOM-CCSD-level accuracy for core-hole spectra

Computes accurate x-ray absorption spectra efficiently

Abstract

The problem of orbital relaxation in computational core-hole spectroscopies, including x-ray absorption and x-ray photoionization, has long plagued linear response approaches, including equation-of-motion coupled cluster with singles and doubles (EOM-CCSD). Instead of addressing this problem by including additional electron correlation, we propose an explicit treatment of orbital relaxation via the use of "transition potential" reference orbitals, leading to a transition-potential coupled cluster (TP-CC) family of methods. One member of this family in particular, TP-CCSD(1/2), is found to essentially eliminate the orbital relaxation error and achieve the same level of accuracy for core-hole spectra as is typically expected of EOM-CCSD in the valence region. These results show that very accurate x-ray absorption spectra for molecules with first-row atoms can be computed at a cost essentially the same as that for EOM-CCSD.