ON THE EQUATION OF STATE OF COMPRESSED LIQUIDS AND SOLIDS
NAVAL ORDNANCE LAB WHITE OAK MD
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The work of van der Waals on gases and Mie and Gruneisen on solids produce equations of state of the form p Gv,T NkTv po v. Many more recent theoretical studies have led to results expressible in the same form. Despite this fact it has been almost a universal fad to describe equations of state through the dimensionless compressibility factor, Fv,T pvNkT instead. This paper shows that much useful information is discarded when the latter form is used. An analysis of po and Gv,T for the Lennard-Jones Devonshire free volume theory and the equation of state results obtained by the Monte Carlo molecular dynamics method has shown that both studies lead to essentially the Mie-Gruneisen equation at high density when the temperature is low enough. At higher temperatures for high density and for all temperatures at lower densities the two theories come close to the usual theories for dense fluids. The functional relations for Gv,T are sufficiently simple to be replaced by analytic functions to facilitate application of the theories to practical problems. It appears that empirical improvements on the original theories can also be made on the basis of new knowledge about the states under consideration. For illustration an analytic fit to the Monte Carlo result for a Lennard-Jones 6-12 potential is presented. A breakdown of Lennard-Jones result for the second virial coefficient is appended.
- Physical Chemistry