  We discuss Molecular Dynamics (MD) computer simulations of tetracosane
(C24H50) monolayer physisorbed onto a graphite surface. The alkane molecules
are simulated with explicit hydrogens, and the graphite substrate is
represented as an all-atom struc-ture having six graphene layers. The
tetracosane dynamics modeled in the fully ato-mistic manner agree well with
experiment. The low-temperature ordered solid orga-nizes in rectangular
centered structure, incommensurate with underlying graphite. Above T = 200 K,
as the molecules start to lose their translational and orientational order via
gauche defects formation, a weak smectic mesophase (observed experimentally but
never reproduced in United Atom (UA) simulations) appears. The phase behavior
of the adsorbed layer is critically sensitive to the way the electrostatic
interactions is included in the model. If the electrostatic charges are set to
zero (as it is in UA force field), the melting temperature increases by ~70 K
with respect to the experimental value. When the non-bonded 1-4 interaction is
not scaled, the melting temperature decreases by ~90 K. If the scaling factor
is set to 0.5, the melting occurs at T = 350 K, in very good agreement with
experimental data. PACS number: 82.45.Mp, 64.70.dj
