Anisotropic Anharmonic Vibrations of the Surface S-Ni and Cl-Ni Bonds in c(2×2)S and Cl/Ni(100) Systems Studied by Molecular Dynamics

The vibrational anisotropy and anharmonicity of the surface adsorbate-substrate bonds in c(2 x 2)S and Cl/Ni(100) systems were investigated by means of classical molecular dynamics calculations. The obtained results were compared to those experimentally given by surface extended X-ray absorption fine structure and high-resolution electron energy loss spectroscopies. Good agreement between calculated and experimental results indicates high reliability of the present method. The calculations allow us to distinguish the component of motions parallel to the surface from the normal one. In both systems, the mean-square displacements of the adsorbates were found to be noticeably greater in the normal direction than in the lateral one. On the other hand, it was revealed that the mean-square relative displacement concerning the S-Ni pair is enhanced in the vertical direction, while that of the Cl-Ni one shows less directional dependence. Such a difference can simply be understood from the local surface geometries.

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