Abstract
Using both classical and quantum mechanical Monte Carlo methods, a number of properties are investigated for a single hydrogen atom adsorbed on palladium and nickel clusters. In particular, the geometries, the preferred binding sites, site specific hydrogen normal mode frequencies, and finite temperature effects in clusters from two to ten metal atoms are examined. Our studies indicate that hydrogen is localized in the present systems. The preferred hydrogen binding sites are found to be tetrahedral in clusters with five or fewer metal atoms and octahedral for clusters of six to ten atoms. The exceptions to this rule are Ni9H and Pd9H for which the outside, threefold hollow and the inside tetrahedral sites are preferred, respectively. Hydrogen induced ‘‘reconstruction’’ of bare cluster geometries is seen in seven and ten-atom clusters.
Highlights
Hydrogen/metal systems represent an interesting and important class of materials
Understanding the structure and dynamics of these hydrogen/metal systems is central to obtaining a detailed understanding of a variety of technologically significant areas
Our purpose is to examine a variety of properties of nickel and palladium systems ranging from two to ten-metal atoms
Summary
Hydrogen/metal systems represent an interesting and important class of materials. Hydrogen’s small mass and uniquely large isotopic variation, for example, give rise to a number of intrinsically quantum mechanical many-body phenomena. Our purpose is to examine a variety of properties of nickel and palladium systems ranging from two to ten-metal atoms Chosen because they constitute interesting dynamical extremes in the bulk,[2,3] these two fcc metals exhibit a variety of cluster geometries for different cluster sizes. Using a combination of classical and quantum Monte Carlo methods, we determine the geometries, preferred hydrogen binding sites, and site variation of hydrogen normal mode frequencies as a function of cluster size. Path integral Monte Carlo methods are utilized to study finite temperature effects. Quantum mechanical effects on the ground state structure and hydrogen binding are examined in Sections IV and V through the use of normal modes, zero-point energy analysis, and diffusion Monte Carlo methods, respectively.
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