Intermolecular potential model Hamiltonians for Gas–Liquid coexistence

Woodcock, Leslie

http://hdl.handle.net/10400.1/18263

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Authors

Woodcock, Leslie

Abstract(s)

A fundamental, hitherto unanswered, question in liquid-state physics is: "What is the minimum requirement of a molecular interaction Hamiltonian for the existence of a stable liquid that can coexist with its vapor phase?". It has been the subject of speculation in the thermophysical property literature since Hagen et al. (Nature 1993) reported ’no liquid phase’ in a computer site–site pairwise model Hamiltonian for C60. In more recent reports we have found that for simple fuids, with spherical, pairwise model Hamiltonians there exists a supercritical mesophase colloidal description of gas–liquid coexistence with a T-p density-surface critical divide being defned thermodynamically by the intersection of percolation loci. We have also reported compelling experimental evidence for the existence of a pre-freezing percolation transition whence hetero-phase fuctuations of micro-crystallites percolate equilibrium liquid state phase volume. These percolation phenomena can explain the apparent disappearance of the boiling line at fnite range of attraction. As the attractive range shortens, the interception of the percolation line that defne the critical-line between two-phase coexistence, and one-phase supercritical mesophase, shifts to lower T. It then intercepts with the pre-freezing percolation line, to trigger a triple point of gas, liquid and solid states, all at the same T,p-state hence also the same chemical potential. Consequently, all model pairwise classical molecular Hamiltonians with a fnite size, plus attractive term, however short-range, or however weak, exhibit a triple point with a liquid–vapor coexisting state at a sufcient low temperature.