Semiempirical models for image electrostatics. I. Bare external charge

A modified semiempirical Pariser-Parr-Pople (PPP) model for the simulation of dielectric properties of metal is developed and analyzed. The model Hamiltonian exactly described the long-range electrostatic interactions. A direct minimization self-consistent field (SCF) method is modified for fast convergence of the wave functions of the large clusters. The density reduction allowed the use of smaller magnitude off-diagonal one-electron matrix elements, which largely changed the spectral density of the SCF orbitals. The model Hamiltonian is used for the study of the interaction potential between the charged molecules and the dielectric and metallic surfaces.