The role of attractive many-body interaction in the gas–liquid transition of mercury

Abstract

The equation of state for expanded fluid mercury based on the variational associating fluidtheory is developed to elucidate the mechanisms of the gas–liquid transition in terms ofmicroscopic interatomic interaction. The theory describes the interaction of anatom with its neighbouring atoms through an effective many-body potential,which is constructed through quantum-chemical calculations of cohesive energiesfor selected geometries of clusters and bulk crystals. The overall feature of theobserved gas–liquid coexistence curve is reproduced accurately without introducingphenomenological adjustable parameters. It is shown that the local aggregation of atomsproduces a strong cohesive force due to a change in the local electronic states, whichplays a crucial role in the gas–liquid transition. The predicted phase behaviour isconsistent with the picture of inhomogeneous expansion, in which the averagecoordination number is nearly proportional to the average density along the coexistencecurve.