Hydrogen interactions and dynamics on metal surfaces and in bulk metals are of interest both technologically and fundamentally. The light mass of hydrogen highlights quantum effects, which are called for to explain peculiar observations related to hydrogen diffusion, vibrational observations, electron-energy loss spectra, photoemission, and thermal desorption.
In this study, the finite temperature quantum behavior of hydrogen adsorbates on Ni(001) surface and small clusters is simulated using path-integral Monte Carlo technique. All the atomic interactions adsorbate–surface and adsorbate–adsorbate interactions are described by the many-body alloy potential form. Temperatures 100 K and 300 K and varying surface coverages are considered. We analyze the distribution functions of atoms and related energetics as a function of number of atoms and temperature. Differences between quantum and classical behavior of hydrogen are compared.
At low temperatures, the quantum delocalization of the adsorbates is considerable, and therefore, temperature dependence of distributions is weak. At T=300 K, however, the H–H interaction has a considerable effect on the distributions and energetics. In contrast, by using the classical description of the hydrogen adsorbates both temperature and coverage dependencies become strong in distribution at all temperatures. At T=100 K, the quantum adsorbates are lying in the circular ground state, exhibiting harmonic like confinement. Thus, the adsorbate–adsorbate interaction is rather small in both cases. Only a slight spreading of the distributions can be observed with increasing temperature.
Refs.:
M. Leino, J. Nieminen and T.T. Rantala, Surf. Sci., 600, 1860(2006);
M. Leino, I. Kylänpää and T.T. Rantala, Surf. Sci., 601, 1246(2007). |