Structure and Layer Interaction in Carbon Monofluoride and Graphane: A Comparative Computational Study

Carbon monofluoride (CF) and graphane are two very different materials from the practical point of view, but the basic chemical motifs of these materials are closely related: both can be described as two-dimensional polycyclic (fluoro-/hydro-)carbons. However, the actual experimental data on the structure of these materials is ambiguous ((CF)) or scarce (graphane). Herein, we report a detailed computational study of structure of (CF) and graphane, both in a monolayer configuration and in three-dimensional stacked arrangements. A crucial point in achieving a proper description of layer interactions is the use of a nonlocal density functional to describe long-range dispersion attraction from first principles. We find strong qualitative and quantitative similarities between the two materials in both conformational energetics (including a gauche-chair conformational motif not considered in previous studies) and layer stacking arrangements. A molecular mechanics force field is derived for (CF) that performs exceptionally well at reproducing our quantum chemical results and fits into a very general OPLS/AA molecular mechanics framework. The combined results of quantum chemical calculations and classical molecular dynamics simulations using the new force field suggest a pathway to explain the too-small experimental in-plane lattice constant values observed in these materials, as well as the variation of interlayer distance in (CF), on the common basis of conformational disorder.