Theory of Hydrogen Quantum Diffusion
Sammanfattning: Atomic hydrogen adsorbed on a metal surface is one of the simplest possible examples of chemisorption, yet it is very challenging. The adsorption and the very elementary process of surface diffusion, a single atomic jump, have been investigated theoretically using several methods. The system that has been studied is hydrogen on the (001) surface of nickel, a system which has been subject to extensive research in the past, experimental as well as theoretical.The adsorption geometry and potential energy surface have been calculated using a pseudopotential plane-wave method, which is a first-principles approach to the problem. The potential energy surface hereby obtained has been exploited to develop a model potential which accurately reproduces the first-principles data. The model potential has in turn been employed to address the following problems, which are still impossible to treat using first-principles methods.
- The vibrational excitation energies and bandwidths for hydrogen and deuterium, by solving the Schrödinger equation.
- The relaxation energies by self-consistently relaxing the surface and solving the Schrödinger equation for hydrogen and deuterium on it.
- The diffusion coefficients for hydrogen and deuterium at different temperatures using the path-centroid formulation of quantum transition-state theory.
- The isotope effect in hydrogen surface diffusion.
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