The lattice energy of hydrogen cyanide

Abstract

The lattice energies of the high and low temperature forms of crystalline HCN have been calculated as a sum of long-range and short-range interactions. The former consist of electrostatic, inductive and dispersive terms whose values are calculated using a molecular SCF wave function combined with experimental values of the dipole moment and polarizability tensor. The short-range energy is divided into Coulomb and exchange terms, the former being estimated by representing the molecular electron density as a set of spherical atomic charge distributions and the latter being taken as proportional to a function closely related to the intermolecular overlap. The constant of proportionality was chosen to reproduce the experimental lattice energy and the calculated potential energy was then found to be minimized at values of the cell dimensions close to the experimental values. The binding in the HCN dimer is also discussed.