Partial fourth order schemes of triples in Fock-space coupled-cluster theory: Ionization potentials of ozone

In this paper, three lowest vertical ionization potentials of ozone molecule are presented using four different approximate triples-corrected methods, in addition to the full singles and doubles level, within the Fock-space coupled-cluster theory. One of them is third-order correction and the other three are fourth-order triples approximations, two of which are partial fourth-order corrections. Ozone represents a major challenge due to the multi-reference nature. The value of the partial fourth-order approximations has been highlighted. In particular, we identify a reliable and computationally cheap partial fourth-order scheme.