A BORN-GREEN-YVON INTEGRAL-EQUATION TREATMENT OF A COMPRESSIBLE FLUID

Previous work using the Born-Green-Yvon (BGY) integral equation approach has been extended to investigate the case of a pure compressible lattice fluid, yielding the equation of state as our main result. We show that the BGY equation does a very good to excellent job at fitting the experimental pressure-volume-temperature surface for both small molecules and polymers; the fit parameters are then used to make predictions about thermodynamic properties for the system of interest. We note that two other equations of state can easily be obtained from the BGY equation, and compare results using BGY and other equations of state. We also comment on the agreement between the BGY description in the athermal limit, which is equivalent to Guggenheim's treatment of random mixing, and some lattice Monte Carlo results.