Isotopic effects in chair graphane

Abstract

Graphane is a layered material consisting of a sheet of hydrogenated graphene, with a C:H ratio of 1:1. We study isotopic effects in the properties of chair graphane, where H atoms alternate in a chairlike arrangement on both sides of the carbon layer. We use path-integral molecular dynamics simulations, which allows one to analyze the influence of nuclear quantum effects on equilibrium variables of materials. Finite-temperature properties of graphane are studied in the range 50--1500~K as functions of the isotopic mass of the constituent atoms, using an efficient tight-bonding potential. Results are presented for kinetic and internal energy, atomic mean-square displacements, fluctuations in the C--H bond direction, plus interatomic distances and layer area. At low temperature, substituting ${}^{13}$C for ${}^{12}$C gives a fractional change of $-2.6\times 10^{-4}$ in C--C distance and $-3.9\times 10^{-4}$ in the graphane layer area. Replacing ${}^2$H for ${}^1$H causes a larger fractional change in the C--H bond of $-5.7\times 10^{-3}$. The isotopic effect in C--C bond distance increases (decreases) by applying a tensile (compressive) in-plane stress. These results are interpreted in terms of a quasiharmonic approximation for the vibrational modes. Similarities and differences with isotopic effects in graphene are discussed.

17 pages, 11 figures, 2 tables

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Cited by in corpus (1)

• Quantum effects in two-dimensional silicon carbide