Thermal properties of molecular crystals. I. Heat capacity and thermal expansion

Abstract

The lattice heat capacity Cvs and especially the difference Cps-Cvs of molecular crystals composed of rigid molecules is shown to be well represented by a suitably modified form of the Leibfried and Ludwig theory of anharmonic crystals. Crystals of low packing density (ρ*<0.65) such as benzene require a (fairly large) heat capacity correction for the heat of lattice defect formation. An empirical correction of the theory is proposed to adapt it for the estimation of Cvs of crystals composed of flexible molecules. The expansion coefficient (αs) of molecular crystals composed of rigid molecules at 0.7Tm