Quantum effects in graphene monolayers: Path-integral simulations

TL;DR

This study uses path-integral molecular dynamics to investigate quantum effects on the structural and thermodynamic properties of graphene, revealing that classical motion dominates at finite temperatures despite quantum vibrational contributions.

Contribution

It provides a detailed analysis of quantum versus classical effects in graphene's properties using PIMD, highlighting the significance of quantum effects on atomic vibrations and thermal expansion.

Findings

Quantum effects influence interatomic distances and layer area.

Classical motion dominates over quantum delocalization at finite temperatures.

Thermal expansion coefficient approaches zero as temperature approaches absolute zero.

Abstract

Path-integral molecular dynamics (PIMD) simulations have been carried out to study the influence of quantum dynamics of carbon atoms on the properties of a single graphene layer. Finite-temperature properties were analyzed in the range from 12 to 2000~K, by using the LCBOPII effective potential. To assess the magnitude of quantum effects in structural and thermodynamic properties of graphene, classical molecular dynamics simulations have been also performed. Particular emphasis has been laid on the atomic vibrations along the out-of-plane direction. Even though quantum effects are present in these vibrational modes, we show that at any finite temperature classical-like motion dominates over quantum delocalization, provided that the system size is large enough. Vibrational modes display an appreciable anharmonicity, as derived from a comparison between kinetic and potential energy of the carbon atoms. Nuclear quantum effects are found to be appreciable in the interatomic distance and layer area at finite temperatures. The thermal expansion coefficient resulting from PIMD simulations vanishes in the zero-temperature limit, in agreement with the third law of thermodynamics.