Interpolating between pair-potential systems

TL;DR

This study investigates the structural and dynamical invariance of liquid-model systems during continuous potential interpolations, revealing near-identical hypersurfaces and properties across different pair potentials like Lennard-Jones, WCA, IPL, and Yukawa.

Contribution

It introduces a method to interpolate between pair-potential systems and demonstrates the near invariance of structure and dynamics, providing insights into potential hypersurface similarities.

Findings

LJ to WCA interpolation shows minimal level crossing.

Structure and dynamics remain almost invariant across interpolations.

Shifted-force-cutoff KA system shares hypersurfaces with original.

Abstract

This paper studies liquid-model systems with almost identical constant-potential-energy hypersurfaces. We simulated continuous interpolations between such systems, specifically between the Lennard-Jones (LJ), Weeks-Chandler-Andersen (WCA), exponent 12 inverse-power-law (IPL), and Yukawa (YK) pair-potential systems. Structure and dynamics were monitored via the radial distribution function and the time-dependent mean-square displacement, respectively. In terms of the interpolation parameter lambda, we argue that two systems have very similar constant-potential-energy hypersurfaces if the potential energies of configurations rarely cross when plotted as functions of lambda. Such absence of "level crossing" applies to a very good approximation for the LJ to WCA transformation, and it also applies to a quite good approximation for the LJ to IPL and the YK to YK transformations (the latter varies the screening length). In all cases, structure and dynamics are shown to be almost invariant as functions of lambda. The density is kept constant when lambda is varied. Temperature must generally be adjusted with lambda, which is done by an iterative "reduced-force-matching" method with no free parameters. We also apply the interpolation strategy to two versions of the Kob-Andersen (KA) binary LJ system and show that a recently introduced shifted-force-cutoff version of this system has constant-potential-energy hypersurfaces, which are almost identical to those of the original KA system. This result rationalizes the previously established fact that the two KA versions have virtually identical physics.