The quantitative thermodynamic effect of adding a weak, longhyphen;range attraction to inversehyphen;power repulsive potentials is studied. The resulting phase diagrams exhibit two fluid phases and a solid phase, a critical point, a triple point, and, for sufficiently soft repulsions, an additional solid phase with an additional triple point. The effects of attractions other than van der Waalsrsquo; are studied too by using a simple analytic model for the canonical partition function. Although such models exhibit a wide variety of thermodynamic behavior, they are still not general enough to reproduce the results of highhyphen;temperature measurements on liquid metals.
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