A comparison of excited state properties for iterative approximate triples linear response coupled cluster methods

A computational study of the potential energy curves of the 1Π state of BH, 1Π state of CH+, 1Σu and 1Πu states of C2, 1Π state of CO, and 1Πg and 1Σ−u states of N2 is carried out with the CC3 and CCSDT-3 corrections to EOMEE-CCSD. Good agreement in structure, vibrational frequencies, and excitation energies of these iterative triples-corrected methods with respect to experiment is found for most of these examples. However, deficiencies in the approximate treatment of triples is evident for BH and CH+.