Lennard-Jones fluid, equilibrium phase

In this paper we review a recently developed theoretical method for phase equilibrium calculation which explicitly accounts for strongly orientation-dependent forces. These anisotropic forces are taken into account through a perturbation scheme in which the reference fluid is composed of simple spherical molecules in practice, the known properties of argon, or those of a Lennard-Jones fluid simulated on the computer, may be used. Such a perturbation scheme was first suggested by Pople ( 7) more than twenty years ago, but was not Immediately used for liquid phase calculations because the reference fluid properties were not sufficiently well known. Since 1972 the theory has been extended and improved, and its successful application to liquids of strongly polar or quadrupolar molecules dates from 1974 ( 7) ... 

R0sjorde et al studied the phase transition in a pure fluid using non-equilibrium molecular dynamics simulations (NEMD). The NEMD method solves Newton s equations of motion for several thousand particles in an imaginary box see Hafskjold for a review. The particles interacted with a Lennard-Jones-type pair... 

The application of this approach to the hard-sphere system was presented by Ree and Hoover in a footnote to their paper on the hard-sphere phase diagram. They made a calculation where they used Eq. (2.27) for the solid phase and an accurate equation of state for the fluid phase to obtain results that are in very close agreement with their results from MC simulations. The LJD theory in combination with perturbation theory for the liquid state free energy has been applied to the calculation of solid-fluid equilibrium for the Lennard-Jones 12-6 potential by Henderson and Barker [138] and by Mansoori and Canfield [139]. Ross has applied a similar approch to the exp-6 potential. A similar approach was used for square well potentials by Young [140]. More recent applications have been made to nonspherical molecules [100,141] and mixtures [101,108,109,142]. 

Fig. 9. Volumes of the supercooled fluid and vitreous phases of hard spheres, soft spheres, and Lennard-Jones molecules (at p— 0) relative to their respective crystalline phases as a function of temperature reduced according to the equilibrium freezing temperatures.

The GCMC method was employed, with which the bulk-phase state in equilibrium in the pore system can be clarified. The potential model for fluid-fluid interaction was Lennard-Jones (LJ) 12-6 function modeled for methane = 148.1 K, 0.381 nm). The cut-off distance was which was thought to be large enough to represent fluid with the full LJ potential. Thns no long-range correction was attempted. 

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