Electrostatic energy with lattice vibration

Distortions in molecular solids seem to reflect a compromise between optimal packing or lattice energy, on the one hand, and optimal shape for the molecule, on the other. Deformations follow paths of least resistance which can be discerned theoretically from molecular orbital (MO) studies, semitheoretically from electrostatic or nonbonding models, or empirically from force constants associated with internal vibrations. 

If we ignore the vibrations of the cores, then the total energy within our model is composed of the kinetic energy of the electrons, the electrostatic interaction between the cores, the electron-electron interaction, and the electron-core interaction. If all these are known for a given structural arrangement of cores, then it is possible to compute the energy as a function of lattice structure and separations between atoms. These structural calculations have been done in recent years, and they have allowed structural determination as a function of pressure, which is related to the change in separation between atoms. This topic will be dealt with later. 

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