CASSCF OPTIMIZATION PROBLEM FOR A GROUP OF EXCITED-STATES

A second-order version of the CASSCF approach to the optimization problem for a single (ground or excited) state and a group of excited states (involving, if necessary, also the ground state) is proposed. In contrast to the already existing methods, in the frameworks of our approach, there arises no need in completing the set of states to be optimized to the full basis set of configuration function space. Generation of secondary orbitals in the course of orbital optimization is also not required. All necessary integral transformations are performed only with active orbitals. These certainly attractive features of our approach appear due to employing the Gauss parametrization of average electronic energy domain, which is nonstandard in quantum chemistry.