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We discuss Molecular Dynamics (MD) computer simulations of tetracosane(C24H50) monolayer physisorbed onto a graphite surface. The alkane moleculesare simulated with explicit hydrogens, and the graphite substrate isrepresented as an all-atom struc-ture having six graphene layers. Thetetracosane dynamics modeled in the fully ato-mistic manner agree well withexperiment. The low-temperature ordered solid orga-nizes in rectangularcentered structure, incommensurate with underlying graphite. Above T = 200 K,as the molecules start to lose their translational and orientational order viagauche defects formation, a weak smectic mesophase (observed experimentally butnever reproduced in United Atom (UA) simulations) appears. The phase behaviorof the adsorbed layer is critically sensitive to the way the electrostaticinteractions is included in the model. If the electrostatic charges are set tozero (as it is in UA force field), the melting temperature increases by ~70 Kwith respect to the experimental value. When the non-bonded 1-4 interaction isnot scaled, the melting temperature decreases by ~90 K. If the scaling factoris set to 0.5, the melting occurs at T = 350 K, in very good agreement withexperimental data. PACS number: 82.45.Mp, 64.70.dj

Structural and phase properties of tetracosane (C24H50) monolayers adsorbed on graphite. Explicit Hydrogen Molecular Dynamics study