Drude-Model Calculation of Dispersion Forces. II. The Linear Lattice

Abstract

The London‐van der Waals cohesive energy of a linear lattice is calculated in the dipole‐dipole approximation, including all orders of perturbation. This result is obtained by applying the Born‐von Kármán method to the electronic motions, using a model which represents each molecule as an isotropic harmonic dipole‐oscillator. The dispersion interaction energy of the lattice is expanded in powers of the parameter α/a³ (where α is the molecular polarizability and a the nearest neighbor distance), and is computed up to the eighth order. For values of α/a³ appropriate to actual molecular crystals, the main contribution to the energy comes from the second order. Among the higher order terms, the third order is always important, but for α/a³≥0.06, contributes less than one‐half of the total correction to the second‐order energy.