A self-consistent charge Xα method. I. Theory

On the basis of a local model potential a semiquantitative MO method is suggested combining some basic ideas of the X alpha approximation and the iterative extended Huckel theory. The molecular potential is represented alternatively by the superposition of simplified atomic charge densities or atomic X alpha potentials, and the non-spherical neighbour contributions to the potential are taken into account explicitly. The iteration is a self-consistent charge procedure reducing the computational effort considerably compared to the SCF theories; the method should, therefore, be applicable to large molecules. The approximations are discussed and directions are described by which improvements are possible.