Isotopic effects in chair graphane

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 13C for 12C gives a fractional change of -2.6 x 10-4 in C-C distance and -3.9 x 10-4 in the graphane layer area. Replacing 2H for 1H causes a larger fractional change in the C-H bond of -5.7 x 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.

Automated summary

The study investigates the isotopic effects in graphane, showing notable influences on material properties when substituting different isotopic atoms at low temperatures. Path-integral molecular dynamics simulations reveal the impact of isotopic atoms on equilibrium variables, providing important insights for material research.