Molecular gradients for semiempirical CI wavefunctions with floating occupation molecular orbitals

Configuration Interaction based on floating occupation Hartree–Fock molecular orbitals has proved to be an useful tool in the study of photochemical reactions. In this paper we describe a method for the calculation of the molecular energy gradient of a CI type wavefunction built with orbitals obtained from a semiempirical Hartree–Fock calculation using floating occupation numbers with gaussian broadening. Our method is tested by computing potential energy curves for the acetone photodissociation reaction.