Molecular-dynamics study of the dynamical excitations in commensurate monolayer films of nitrogen molecules on graphite: A test of the corrugation in the nitrogen-graphite potential.

摘要: The dynamical excitations in a commensurate monolayer solid of ${\mathrm{N}}_{2}$ molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well coherent intermediate scattering structure factors calculated at several temperatures wave vectors. Effects out-of-plane motions the formation pinwheel-like structural elements associated with orientational-disorder transition are observed both equilibrium order parameters time-correlation functions. temperature dependence Brillouin-zone-center frequency gap acoustic phonon branches up to melting point agrees experimental observations gives strong support model substrate corrugation energy. Diffusive motion fluid just above has demonstrated from time mean-square displacement two-dimensional diffusion coefficient is estimated be 2--3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ ${\mathrm{cm}}^{2}$/s 75--80 K.