title: Gradients for configuration interaction energies with spin-orbit coupling in a semiempirical framework.
abstract: We present a method for the analytical evaluation of the molecular energy gradient for a semiempirical configuration interaction (CI) wavefunction, taking into account the spin-orbit coupling. We show how to proceed in the simplest case where all the wavefunctions belonging to the CI subspace considered are mixed by the spin-orbit interaction, and we develop an original procedure for the more complex case where only a limited number of CI eigenvectors of the spin-free Hamiltonian are mixed.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35, 56126 Pisa, Italy. granucci@dcci.unipi.it
authors.forename: Giovanni
authors.initials: G
authors.lastname: Granucci
authors.forename: Maurizio
authors.initials: M
authors.lastname: Persico