An efficient first-order CASSCF method based on the renormalized Fock-operator technique

Summary A new efficient first-order CASSCF method (multiconfiguration SCF (self consistent field) in a complete active space) is described. Its main characteristics are (i) use of the generalized Brillouin theorem (Fock-operator method), (ii) renormalization of single excitations, (iii) fast microiterations containing only two-index transformations, i.e. M³N² steps. Convergence is generally reached in eight to twelve macroiterations. The method is applied to several examples (LiH, N₂, AlO) and compared to other MCSCF (multiconfiguration SCF) methods.