Nuclear Quantum Effects Sustain Cooperative Hydride Ion Migration and Restore Arrhenius Behavior in Pnma LaH_3-x

Hydride ion (H^-) conduction materials have attracted significant attention for their potential in advanced clean energy storage and conversion. Moreover, understanding H^- migration mechanisms is essential for controlling ionic transport in these materials and advancing next-generation energy technologies, given the quantum mechanical nature of hydrogen. Here, we investigate the role of nuclear quantum effects (NQEs) by comparing results obtained from thermostated ring polymer molecular dynamics (TRPMD) simulations with those from classical molecular dynamics (MD) simulations using a trained deep potential (DP) model. Our results show that the main manifestation of NQEs is not the conventional quantum tunneling often intuitively expected. Instead, they facilitate the cooperative H^- migration mechanism at low temperatures. This is reflected in the increased mean square displacements (MSDs) and diffusion coefficients observed under these conditions. Notably, the temperature dependence of diffusion coefficients from TRPMD follows Arrhenius behavior, whereas that of classical MD deviates significantly at low temperatures. This work highlights the crucial role of NQEs in governing low-temperature transport and provides fundamental insights for the design of advanced H^- conductors.