Proton diffusion in noble metals

The configurational and activation energies of proton are investigated in noble metals within the framework of many-particle theory. Model pseudopotentials are used to represent the bare ions of the host lattice and the modified Hartree dielectric function which includes the exchange-correlation corrections explicitly, is used for the screening due to conduction electrons. The octahedral position is found to be more stable for the proton, but this is most likely to be trapped into a vacancy if available. The activation energies are found to be in reasonably good agreement with the experimental values for effective proton charges $0.31e$, $0.29e$, and $0.23e$ in copper, silver, and gold, respectively. The configurational and activation energies are found to decrease as the lattice is expanded.