Deformation-diffusion coupled analysis of long-term hydrogen diffusion in nanofilms

The absorption and desorption of hydrogen in nanomaterials can be characterized by an atomic, deformation-diffusion coupled process with a time scale of the order of seconds to hours. This time scale is beyond the time windows of conventional atomistic computational models such as molecular dynamics (MD) and transition state theory based accelerated MD. In this paper, we present a novel, deformation-diffusion coupled computational model basing on non-equilibrium statistical mechanics, which allows long-term simulation of hydrogen absorption and desorption at atomic scale. Specifically, we propose a carefully designed trial Hamiltonian in order to construct our meanfield based approximation, then apply it to investigate the palladium-hydrogen (Pd-H) system. Specifically, here we combine the meanfield model with a discrete kinetic law for hydrogen diffusion in palladium nanofilms. This combination in practice defines the evolution of hydrogen atomic fractions and lattice constants, which facilitates the characterization of the deformation-diffusion process of hydrogen over both space and time. Using the embedded atom model (EAM) potential, we investigate the deformation-diffusion problem of hydrogen desorption and absorption in palladium nanofilms and compare our results with experiments both in equilibrium and non-equilibrium cases.