Molecular dynamics simulations of hexane on graphite at various coverages: the difference explicit hydrogens make

Molecular Dynamics simulations of hexane (C$_{6}$H$_{14})$ adlayers on graphite are carried out for coverages of 0.5 $\le $ \textit{$\rho $ }$\le $ 1 monolayers. The hexanes have explicit hydrogens and the graphite is modeled as an all -- atom, six -- layer structure. Above \textit{$\rho $ }$\cong $ 0.9 the herringbone solid loses orientational order at $T_{1}$ = 140 K $\pm $ 3 K. At \textit{$\rho $} = 0.878 the system presents vacancy patches and $T_{1}$ decreases to ca. 100 K. As coverage decreases further, the vacancy patches become larger and by \textit{$\rho $} = 0.614 the solid is a connected network of randomly oriented domains. All cases show a weak nematic mespohase. The melting temperature is $T_{2}$ = 160 K $\pm $ 3 K and falls to ca. 145 K by \textit{$\rho $} = 0.614. The dynamics and energetics observed demonstrate that the explicit-hydrogen model of hexane is substantially more realistic than the UA approximation.