Electron-gas model for molecular crystals. Application to the alkali and alkaline-earth hydroxides

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Abstract
A theoretical model for calculating the structure and energy of molecular crystals is presented. The model, which requires no empirical parameters, is based on the Gordon-Kim electron-gas model. Many-body effects are incorporated through the mutual overlap of the electronic distributions of all molecules or ions in the neighborhood of a given point in the crystal. Effects of the crystal environment on the molecular properties are approximated by inclusion of an electrostatic potential that mimics the crystal potential in ab initio calculations on the individual component molecules or ions in the crystal. Application is made to a number of alkali and alkaline-earth hydroxide crystals in which the components are taken to be hydroxide ions, and alkali or alkaline-earth cations. The agreement with experiment is good (within 2.5% in lattice constants and 1.1% in lattice dissociation energy). The calculated changes in molecular dipole moment are between 20 and 40%.