Studies of the Lennard-Jones fluid in 2, 3, and 4 dimensions highlight the need for a liquid-state 1/d expansion

TL;DR

This study investigates the virial potential-energy correlation in Lennard-Jones fluids across 2, 3, and 4 dimensions, demonstrating increased correlations with higher dimensions and emphasizing the importance of a 1/d expansion in liquid-state theory.

Contribution

It provides the first numerical evidence of isomorph invariance in four dimensions and highlights the need for a universal 1/d expansion in liquid-state physics.

Findings

Virial potential-energy correlation increases with dimension.

Lennard-Jones systems conform better to hidden-scale-invariance at higher dimensions.

First demonstration of isomorph invariance in four dimensions.

Abstract

The recent theoretical prediction by Maimbourg and Kurchan [arXiv:1603.05023] that for regular pair-potential systems the virial potential-energy correlation coefficient increases towards unity as the dimension $d$ goes to infinity is investigated for the standard 12-6 Lennard-Jones fluid. This is done by computer simulations for $d=2,3,4$ going from the critical point along the critical isotherm/isochore to higher density/temperature. In all cases the virial potential-energy correlation coefficient increases significantly. For a given density and temperature relative to the critical point, with increasing number of dimension the Lennard-Jones system conforms better to the hidden-scale-invariance property characterized by high virial potential-energy correlations (a property that leads to the existence of isomorphs in the thermodynamic phase diagram, implying that it becomes effectively one-dimensional in regard to structure and dynamics). The present paper also gives the first numerical demonstration of isomorph invariance of structure and dynamics in four dimensions. Our findings emphasize the need for a universally applicable $1/d$ expansion in liquid-state theory; we conjecture that the systems known to obey hidden scale invariance in three dimensions are those for which the yet-to-be-developed $1/d$ expansion converges rapidly.