A model for the thermodynamics of simple liquids

The model liquids discussed herein are represented as correlated ensembles of particles, moving around and interacting with strong, short-range forces. A spectrum of local vibrations is introduced for the local, collective movements of particles in such model liquids. The resulting statistics is formally equivalent with that of an ideal gas of bosons in two dimensions, which in turn, as it is well known, leads to a thermodynamics which is equivalent to that of an ideal gas of fermions in two dimensions. The parameters used for describing the statistics of the model are the cohesion energy per particle, the spacing between the energy levels of local vibrations and a constraining volume. The corresponding thermodynamics is derived, with explicit emphasis on both low- and high-temperature regimes. The condensation occurring in the low-temperature limit is discussed.