Loop-Driven Graphical Unitary Group Approach Multiconfiguration Self-Consistent-Field Method with Applications to Water, Ozone, and Cyclopropenyl Radical

摘要

A multiconfiguration self-consistent-field (MCSCF) method based on the loop-driven graphical unitary group approach (LDGUGA) has been developed that combines the best features of the LDGUGA configuration interaction (CI) procedure with the ability to optimize the molecular orbitals. In contrast to traditional MCSCF procedures which are restricted to small configuration sets, our method can handle very large numbers of configurations. Unlike other large configuration list MCSCF procedures, however, the CI expansion is not restricted to being of a particular form (such as in the CASSCF method). The formalism we adopt is an iterative two-step process, that is, during each iteration the CI coefficients are optimized for a fixed guess at the orbital expansion coefficients and then improved orbitals are computed using these CI coefficients.