Abstract
This paper continues the investigation of the exponentially repulsive EXP pair-potential system of Paper I [A. K. Bacher et al., J. Chem. Phys. 149, 114501 (2018)] with a focus on isomorphs in the low-temperature gas and liquid phases. As expected from the EXP system's strong virial potential-energy correlations, the reduced-unit structure and dynamics are isomorph invariant to a good approximation. Three methods for generating isomorphs are compared: the small-step method that is exact in the limit of small density changes and two versions of the direct-isomorph-check method that allows for much larger density changes. Results from the latter two approximate methods are compared to those of the small-step method for each of the three isomorphs generated by 230 one percent density changes, covering one decade of density variation. Both approximate methods work well.
Highlights
This paper and its companion (Paper I, Ref. 1) present an investigation of the exponential (EXP) pair-potential system consisting of identical particles interacting via the purely repulsive pair potential, vEXP(r) = ε e−r/σ . (1)Both papers focus on the region of the thermodynamic phase diagram where temperature is so low that the finite value vEXP(0) plays little role for the physics, i.e., where kBT ε
The fact that the EXP pair-potential system obeys Eq (2) to a good approximation implies that it has isomorphs, which are curves in the phase diagram along which the structure and dynamics are approximately invariant in proper units
We proceed to compare the approximate isomorphs generated from ten successive DIC jumps to what is termed “single state point DIC” (SSDIC)-generated isomorphs that start from the same density ρ1
Summary
This paper and its companion (Paper I, Ref. 1) present an investigation of the exponential (EXP) pair-potential system consisting of identical particles interacting via the purely repulsive pair potential, vEXP(r) = ε e−r/σ Both papers focus on the region of the thermodynamic phase diagram where temperature is so low that the finite value vEXP(0) plays little role for the physics, i.e., where kBT ε. The fact that the EXP pair-potential system obeys Eq (2) to a good approximation implies that it has isomorphs, which are curves in the phase diagram along which the structure and dynamics are approximately invariant in proper units.. 21 and 25; an alternative proof utilizing constant-potential-energy (NVU) dynamics was presented in Paper I.1 Both proofs are based on the fact that under certain conditions a sum of two EXP pair.
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