Q. Is it possible to calculate the excited states of species with a triplet spin ground state, e.g. oxygen atom or oxygen molecule, and what does the input look like?

 

A. It is possible to calculate triplet ground state with SAC-CI method.  However, since the current SAC-CI program starts with the calculation of the closed shell SAC state, the accuracy of the calculation for molecules like O₂ depends on how one defines the closed-shell state.  The accuracy can be improved if you include higher-excited operators in the SAC-CI general-R method.