Surface lattice (100) of Ni. Two minimum-energy sites of fourfold symmetry are marked by Ha and a saddle point of twofold symmetry by Hb. (b) is the hop length of diffusive process.
The plan form and profile chart of H diffusion on Ni(100) lattice. The gray circles represent H atom on different surface sites and the orange circles represent the fixed Ni atoms. Blue circles are Ni atoms treated classically while the red ones are treated quantum mechanically.
Distribution of H and Ni quantum paths on the surface with two coordinate beads ( and ) of H path fixed at the two dividing surfaces. The probabilities are normalized for both H and Ni. The difference between two nearest contour lines for Ni is five times larger than that for H. Solid lines denote H and dotted lines denote Ni.
Arrhenius plots of the rate constants in the range of 40–300 K. Solid line: the QI results for the quantized lattice. Dotted line: the QI results for the rigid lattice. Dot-dashed line: the CVT results for the rigid lattice. Dashed line: the CVT/SCSAG results for the rigid lattice. Dot-dot-dashed line: the CVT/SCSAG results for the quantized lattice.
Free energy profiles at 200 K. The solid, dotted, and dashed lines correspond to the quantized, classical, and rigid lattices, respectively.
Arrhenius plots of the diffusion coefficients in the range of 40–300 K. Solid line: the QI results for quantized lattice. Dotted line: the QI results for rigid lattice. Dashed line: the CVT/SCSAG results for the rigid lattice. Pluses, crosses, squares, and circles are experimental results of Lee et al., Gomer et al., Mullins et al. and George et al., respectively.
The positions of two dividing surfaces.
Rate constants (unit is , powers of 10 are in parentheses, and the rates are only for a one reaction path) for the H/Ni(100) system.
The free energy barriers (kcal/mol) and the prefactors (powers of 10 are in parentheses).
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