LI. The communal entropy of dense systems

Summary This paper contains an approximate method of calculating the communal entropy of an assembly of monatomic particles. The method of dealing with dense systems may be regarded as an extension of that used by Lennard-Jones and Devonshire in their theory of liquids and dense gases. The available volume is divided into cells and the communal free energy expressed in terms of a set of parameters related to the probability of two, three or more particles occupying a given cell simultaneously. Application to an assembly of rigid spheres leads to the conclusion that the communal entropy does not become appreciable until the available volume is over five times that of a close-packed assembly. This suggests that, for more accurate intermolecular potentials, the communal entropy is practically zero in the solid and liquid states, but that the extra terms in the free energy may have an appreciable effect on the calculated critical constants and vapour pressures.