Quantum mechanical rate constants via path integrals: diffusion of hydrogen atoms on a W(100) surface

Using Monte Carlo path integrals methods quantum mechanical rate constants have been calculated for diffusion of H atoms on a model W(100) surface. The most interesting aspect of the present work is that it includes the effect of surface atom motion, i.e., phonons, on the H atom tunneling dynamics. Although the description is fully quantum mechanical, the phonons enter the present path integral treatment in a way very similar to how they appear in the classical generalized Langevin models; the present formulation thus provides the correct quantum mechanical analogue to classical frictional effects. The principal qualitative results shown by the calculations is that surface atom motion increases the rate of H-atom tunneling from one stable site on the surface to another. 23 references, 3 figures, 2 tables