THEORY OF DEFECTS IN CONDUCTING POLYMERS .1. THEORETICAL PRINCIPLES AND SIMPLE APPLICATIONS

We describe a method for solving simultaneously the Hartree-Fock equations of motion in the zero differential overlap approximation for the electronic structure of a molecule and the dynamical equations of motion for its atoms. Our approach is similar to that of Car and Parrinello in that we optimize the electronic structure and the geometry simultaneously, but differs in that we make a chosen number of iterations towards electronic self-consistency at each geometry rather than treating the electron wavefunctions as dynamical variables. We give examples of the use of the method to calculate the equilibrium geometries, dipole moments, molecular polarizabilities and vibrational frequencies of small molecules. In the following paper we apply this approach to problems of defect processes in conducting polymers.