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. (C) 2000 Published by Elsevier Science B.V.