Based on quasi complete active space self-consistent field (QCAS-SCF) reference functions, a quasi-degenerate perturbation theory (QDPT) was presented. Using a diagrammatic approach, a computational scheme to second-order was described. Second-order effective Hamiltonian consisted of the contribution from external excitation which involved core/or/and virtual orbitals, and internal excitations, which involved only active orbitals.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry