MCSCF or CASSCF calculations usually account only for a small percentage of the dynamical correlation energy. Therefore, in order to obtain accurate results, subsequent correlation treatments are possible. This can either be done by multireference configuration interaction (MRCI) or by multireference perturbation theory (MRPT). The latter is simpler and much cheaper, but also less reliable than MRCI.

- 8.1 Multireference configuration interaction (MRCI)
- 8.2 Multireference perturbation theory, CASPT2, CASPT3

molpro@molpro.net 2017-09-24