Negative thermal expansion in single-component systems with isotropic interactions

TL;DR

This paper introduces an isotropic interaction potential that induces negative thermal expansion in single-component systems across various dimensions, a phenomenon previously observed mainly in directional interaction systems.

Contribution

The authors develop and optimize a novel isotropic potential that demonstrates negative thermal expansion in equilibrium many-particle systems, a first in such isotropic single-component systems.

Findings

The potential produces NTE behavior over a wide temperature and pressure range.

Simulations show NTE transitions to positive expansion before melting.

Compared to Lennard-Jones systems, the new potential exhibits anomalous expansion behavior.

Abstract

We have devised an isotropic interaction potential that gives rise to negative thermal expansion (NTE) behavior in equilibrium many-particle systems in both two and three dimensions over a wide temperature and pressure range (including zero pressure). An optimization procedure is used in order to find a potential that yields a strong NTE effect. A key feature of the potential that gives rise to this behavior is the softened interior of its basin of attraction. Although such anomalous behavior is well known in material systems with directional interactions (e.g., zirconium tungstate), to our knowledge this is the first time that NTE behavior has been established to occur in single-component many-particle systems for isotropic interactions. Using constant-pressure Monte Carlo simulations, we show that as the temperature is increased, the system exhibits negative, zero and then positive thermal expansion before melting (for both two- and three-dimensional systems). The behavior is explicitly compared to that of a Lennard-Jones system, which exhibits typical expansion upon heating for all temperatures and pressures.