A model for charge distribution in the gas and solid phases

Abstract

A technique is developed to model the change in molecular charge distribution as a system moves from the gas phase to the solid phase. The change in charge distribution is modelled by mixing occupied and unoccupied orbitals of the gas-phase system. The overall energy and charge distribution calculated is a function of a mixing parameter, θ. The overall energy is comprised of two terms, that due to the internal molecular energy and that due to the electrostatic interaction of charged species in the solid state, which stabilises the more ionic structures. The overall energy is calculated as a function of θ, and the lowest-energy arrangement is identified. Initial calculations are made on the system in the gas phase, using semi-empirical Hartree-Fock theory. The results produced by this calculation are then input into the model, which calculates the energy and charge distribution for the solid phase. The model has been applied to the LiF system. The change in charge distribution for this system is not as large as anticipated and the reasons for this are discussed.