path-integral simulations of hydrogen-isotope diffusion in face-centred cubic metals

Kimizuka, Hajime*; Ogata, Shigenobu*; Thomsen, B.  ; Shiga, Motoyuki   

Calculations of hydrogen isotope diffusion coefficients for face-centred cubic lattice metals using path integral methods show that the temperature dependence of the diffusion coefficients has an unusual shape. This is due to the competition between nuclear quantum effects with different temperature dependence, which explains the unusual crossover mechanism between the normal and inverse isotope effects. We also present the results of a path integral simulation that describes approximate quantum dynamics using machine learning-based interatomic potentials with almost the same accuracy as density functional theory calculations. This computational method paves the way for understanding the quantum behaviour of hydrogen isotopes in various solid-state materials.