Mean square force in simple liquids and solids from isotope effect studies

Abstract

The*vapor pressure isotope effect in the rare gases, 2 neon, argon, and krypton, has been used to determine <V U>, mean Laplacian of the intermolecular potential, as a function of temperature in the rare gas solids and liquids.An abrupt discontinuity is found at the triple point which is closely correlated with the density change on melting.The mean square force between rare gas atoms in the liquid is linear in p, the density, divided by T from the triple point to near the critical temperature. Deviations of the order of ten per cent have been found from the law of » 2 corresponding states for <V U>. It is shown that excellent 2 agreement is obtained between measured values of <V U> and radial distribution functions calculated by molecular dynamics and statistical mechanics.

Isomorph theory of physical aging

“…Due to its isomorphs an R-simple system has a phase diagram that is basically one-dimensional in regard to many properties. This excludes complex behavior; hence the name "R-simple" for systems that have isomorphs (the term "simple system" implies a system of particles interacting via pair potentials [42][43][44][45][46][47][48][49][50][51][52][53][54][55]).…”