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Title: Statistical mechanics of Roskilde liquids: Configurational adiabats, specific heat contours, and density dependence of the scaling exponent

We derive exact results for the rate of change of thermodynamic quantities, in particular, the configurational specific heat at constant volume, C{sub V}, along configurational adiabats (curves of constant excess entropy S{sub ex}). Such curves are designated isomorphs for so-called Roskilde liquids, in view of the invariance of various structural and dynamical quantities along them. The slope of the isomorphs in a double logarithmic representation of the density-temperature phase diagram, γ, can be interpreted as one third of an effective inverse power-law potential exponent. We show that in liquids where γ increases (decreases) with density, the contours of C{sub V} have smaller (larger) slope than configurational adiabats. We clarify also the connection between γ and the pair potential. A fluctuation formula for the slope of the C{sub V}-contours is derived. The theoretical results are supported with data from computer simulations of two systems, the Lennard-Jones fluid, and the Girifalco fluid. The sign of dγ/dρ is thus a third key parameter in characterizing Roskilde liquids, after γ and the virial-potential energy correlation coefficient R. To go beyond isomorph theory we compare invariance of a dynamical quantity, the self-diffusion coefficient, along adiabats and C{sub V}-contours, finding it more invariant along adiabats.
Authors:
; ; ; ;  [1]
  1. DNRF Center “Glass and Time,” IMFUFA, Dept. of Sciences, Roskilde University, P. O. Box 260, DK-4000 Roskilde (Denmark)
Publication Date:
OSTI Identifier:
22251446
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 139; Journal Issue: 18; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMPUTERIZED SIMULATION; DENSITY; ENTROPY; FLUCTUATIONS; LIQUIDS; PHASE DIAGRAMS; POTENTIAL ENERGY; POTENTIALS; SELF-DIFFUSION; SPECIFIC HEAT; STATISTICAL MECHANICS