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

F. Y. Hansen and L. W. Bruch
Phys. Rev. B 51, 2515 – Published 15 January 1995
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Abstract

The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been calculated at several temperatures and wave vectors. Effects of out-of-plane motions and the formation of pinwheel-like structural elements associated with the orientational-disorder transition are observed both in the equilibrium order parameters and in the time-correlation functions. The calculated temperature dependence of the Brillouin-zone-center frequency gap in the acoustic phonon branches up to the melting point agrees well with the experimental observations and gives strong support to a model of the substrate corrugation energy. Diffusive motion in the fluid just above the melting point has been demonstrated from the time dependence of the mean-square displacement of the molecules and the two-dimensional diffusion coefficient is estimated to be 2–3×105 cm2/s at 75–80 K.

  • Received 19 September 1994

DOI:https://doi.org/10.1103/PhysRevB.51.2515

©1995 American Physical Society

Authors & Affiliations

F. Y. Hansen

  • Department of Physical Chemistry, Technical University of Denmark, DTU 206, DK-2800, Lyngby, Denmark

L. W. Bruch

  • Department of Physics, University of Wisconsin(enMadison, Madison, Wisconsin 53706

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Vol. 51, Iss. 4 — 15 January 1995

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