Two distinct non-Arrhenius behaviors of hydrogen diffusivities in fcc aluminum, silver, and copper determined by path integral simulations

Kimizuka, Hajime*; Shiga, Motoyuki   

Nuclear quantum effects are a non-negligible factor in the dynamic behavior of hydrogen in metals. In this study, we investigated the hydrogen diffusion in the face-centered cubic metals Al, Ag, and Cu using a first-principles integral molecular dynamics simulation that takes into account the nuclear quantum effects. It was found that the temperature dependence of hydrogen diffusion in Ag and Cu is inverted S-shaped, while the temperature dependence of hydrogen diffusion in Al is C-shaped. This difference is due to the fact that the most stable position of hydrogen is the octahedral site in Ag and Cu, while it is the tetrahedral site in Al. Therefore, it is found that the nuclear quantum effects of hydrogen diffusion (zero-point oscillation and tunneling) differ qualitatively depending on metals with different stable sites.