The coupled-cluster single, double, and triple excitation model for open-shell single reference functions

The CCSDT model for general single determinant reference functions for open and closed-shell electronic states has been implemented for the first time and has been used to compute the electron affinity of the F atom, the CH2, 3B1–1A1 energy difference, and the ionization potentials of 1A1 CH2. The results compare very well with FCI and are markedly superior to those of simpler coupled-cluster methods.