Theoretical calculation and comparison of H diffusion on Cu(111), Ni(111), Pd(111), and Au(111)

We calculated the diffusion coefficient of hydrogen (H) on metal surfaces. In our method, the potential energy surface obtained from the ab initio calculations is diagonalized to calculate the wave function of H, which is used to obtain the free energy surface. We combined this free energy surface with transition state theory to obtain the diffusion coefficient. This combination of the free energy surface and transition state theory allowed us to include quantum effects and entropy effects in the transition state theory without stochastic simulations. In addition, by defining diffusion sited from the free energy surface rather than the potential energy surface, the shape and size of the diffusion sites became temperature dependent. The calculated diffusion coefficients were compared with previous studies. Although the present method reproduced the results at and above the crossover temperatures, it was found that more sophisticated quantum mechanical schemes are required at cryogenic temperatures.

Automated summary

We calculated the diffusion coefficient of hydrogen on metal surfaces using a method that combines diagonalization of the potential energy surface with transition state theory. By including quantum effects and entropy effects in the transition state theory without stochastic simulations, our method provides more accurate results. However, more sophisticated quantum mechanical schemes are needed for cryogenic temperatures.