Influence of mass difference on dynamic properties of isotope mixtures

TL;DR

This study uses molecular dynamics simulations to explore how mass differences in isotope mixtures affect their dynamic properties, revealing significant impacts and challenging existing universal diffusion scaling laws.

Contribution

It provides new insights into the influence of mass heterogeneity on dynamic properties and offers a counterexample to a proposed universal diffusion law.

Findings

Dynamic properties are significantly affected by mass difference.

Existence of 'critical' mass difference values affecting behavior.

Contradicts a proposed universal diffusion scaling law.

Abstract

We present the results of a Molecular Dynamics computer simulations of a two component isotope mixture of Lennard-Jones particles, monodisperse in size but different in masses, at a fixed average density and temperature. We study changes in properties that result from mass heterogeneity, by measuring the pair distribution function, diffusion coefficient, velocity autocorrelation function, non-Gaussian and isotope effect parameters, as functions of the degree of mass difference. Our results show that if static properties are not influenced by a variation of mass variation, the dynamic properties are significantly affected and even exhibit the presence of ``critical'' values in the mass difference. We also demonstrate that our model gives a simple contra example to a recently proposed a universal scaling law for atomic diffusion in condensed matter [M. Dzugudov, Nature, v.381, 137 (1996)].