Quantum effects in structural and elastic properties of graphite: Path-integral simulations

TL;DR

This study uses path-integral molecular dynamics to investigate quantum effects on the structural and elastic properties of graphite, revealing significant quantum contributions up to temperatures above 300 K.

Contribution

It introduces quantum simulations to accurately model graphite's properties, highlighting the importance of quantum effects in thermal expansion and elasticity.

Findings

Quantum effects significantly influence graphite's elastic constants.

Zero-point motion reduces bulk modulus and Poisson's ratio.

Quantum corrections can exceed 20% in stiffness constants.

Abstract

Graphite, as a well-known carbon-based solid, is a paradigmatic example of the so-called van der Waals layered materials, which display a large anisotropy in their physical properties. Here we study quantum effects in structural and elastic properties of graphite by using path-integral molecular dynamics simulations in the temperature range from 50 to 1500~K. This method takes into account quantization and anharmonicity of vibrational modes in the material. Our results are compared with those found by using classical molecular dynamics simulations. We analyze the volume and in-plane area as functions of temperature and external stress. The quantum motion is essential to correctly describe the in-plane and out-of-plane thermal expansion. Quantum effects cause also changes in the elastic properties of graphite with respect to a classical model. At low temperature we find an appreciable decrease in the linear elastic constants, mainly in $C_{12}$ and $C_{44}$. Quantum corrections in stiffness constants can be in some cases even larger than 20\%. The bulk modulus and Poisson's ratio are reduced in a 4\% and 19\%, respectively, due to zero-point motion of the C atoms. These quantum effects in structural and elastic properties of graphite are nonnegligible up to temperatures higher than 300~K.