  We present the first large-scale molecular dynamics simulations of hexane on
graphite that completely reproduces all experimental features of the melting
transition. The canonical ensemble simulations required and used the most
realistic model of the system: (i) fully atomistic representation of hexane;
(ii) explicit site-by-site interaction with carbon atoms in graphite; (iii)
CHARMM force field with carefully chosen adjustable parameters of non-bonded
interaction; (iv) numerous $\ge$ 100 ns runs, requiring a total computation
time of ca. 10 CPU-years. This has allowed us to determine correctly the
mechanism of the transition: molecular reorientation within lamellae without
perturbation of the overall adsorbed film structure. We observe that the melted
phase has a dynamically reorienting domain-type structure whose orientations
reflect that of graphite.
