Transition-potential coupled cluster

The problem of orbital relaxation in computational core-hole spectroscopies, including x-ray absorption and photoionization, has long plagued linear response approaches, equation-of-motion coupled cluster with singles doubles (EOM-CCSD). Instead addressing this by additional electron correlation, we propose an explicit treatment via the use “transition potential” reference orbitals, leading to a transition-potential (TP-CC) family methods. One member family, particular, TP-CCSD(12), is found essentially eliminate error achieve same level accuracy for spectra as typically expected EOM-CCSD valence region. These results show that very accurate molecules first-row atoms can be computed at cost EOM-CCSD.