NEVPT2 must follow a CAS-SCF or CAS-CI calculation. The command
has to be specified to carry out a second-order perturbation calculation. NEVPT2 is part of the MRCI program and uses the options of the latter. Of particular relevance are the options CORE, CLOSED, OCC, WF and STATE of the MRCI program. There is, at the moment, only one option specific to NEVPT2 which can be provided by the user:
An example is provided where the energies of the ground state and of the first () excited state of formaldehyde are calculated.