Understanding the transport of hydrogen within metals is crucial for the advancement of energy storage and the mitigation of hydrogen embrittlement. Using nanosized palladium particles as a model, recent experimental studies have revealed several highly nonlinear phenomena that occur over a long period of time. The time scale of these phenomena is beyond the capability of established atomistic models. In this work, we present the application of a new model, referred to as diffusive molecular dynamics (DMD), to simulating long-term diffusive mass transport at atomistic length scale. Specifically, we validate the model for the long-term dynamics of a single hydrogen atom on palladium lattice. We show that the DMD result is in satisfactory agreement with the result of the classical random walk model. Then, we apply the DMD model to simulate the absorption of hydrogen by a palladium nanocube with an edge length of 16 nm. We show that the absorption process is dominated by the propagation of a sharp, coherent α/β hydride phase boundary. We also characterize the local lattice deformation near the dynamic phase boundary using the mean positions of the palladium and hydrogen atoms.
We present evidence of strong steric interference in bilayer graphene containing offset point dislocations. Calculations are carried out with Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) using the Long-Range Carbon Bond-Order Potential (LCBOP) potential of Los et al.. We start by validating the potential in the harmonic response by comparing the predicted phonon dispersion curves to experimental data and other potentials. The requisite force constants are derived by linearization of the potential and are presented in full form. We then continue to validate the potential in applications involving the formation of dislocation dipoles and quadrupoles in monolayer configurations. Finally, we evaluate a number of dislocation quadrupole configurations in monolayer and bilayer graphene and document strong steric interactions due to out-of-plane displacements when the dislocations on the individual layers are sufficiently offset with respect to each other.
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