Statistical mechanics of deformable molecular liquids: Thermal expansion and isomerization of diatomic molecules

Equilibrium two-body correlations in liquids composed of deformable molecules are formulated with use of the density-functional theory and the interaction site formalism. As applications, we study two model systems, liquid nitrogen and simplified liquid n butane, in which each molecule has two stable bond lengths. The latter may be considered as a toy model to study conformational equilibrium.