Development of an inter-atomic potential for the Pd-H binary system.

Abstract

Ongoing research at Sandia National Laboratories has been in the area of developing models and simulation methods that can be used to uncover and illuminate the material defects created during He bubble growth in aging bulk metal tritides. Previous efforts have used molecular dynamics calculations to examine the physical mechanisms by which growing He bubbles in a Pd metal lattice create material defects. However, these efforts focused only on the growth of He bubbles in pure Pd and not on bubble growth in the material of interest, palladium tritide (PdT), or its non-radioactive isotope palladium hydride (PdH). The reason for this is that existing inter-atomic potentials do not adequately describe the thermodynamics of the Pd-H system, which includes a miscibility gap that leads to phase separation of the dilute (alpha) and concentrated (beta) alloys of H in Pd at room temperature. This document will report the results of research to either find or develop inter-atomic potentials for the Pd-H and Pd-T systems, including our efforts to use experimental data and density functional theory calculations to create an inter-atomic potential for this unique metal alloy system. This research was funded by the Physics and Engineering Models sub-program of the Advanced Simulation and Computing program conducted at Sandia National Laboratories.

Solution-Phase Synthesis of PdH0.706 Nanocubes with Enhanced Stability and Activity toward Formic Acid Oxidation

“…In modeling the PdH 0.706 phase, we adopted the PdH 0.75 model phase with the bottom three layers of the slab fixed at the optimized lattice constant of bulk material (4.155 Å), which is in good agreement with the experimental value of 4.059 Å for the PdH 0.75 phase. 38,39 The construction of this model avoids the use of excessively large unit cells needed to capture the PdH 0.706 stoichiometry, while still providing useful insights for rationalizing the effect of Pd-hydride phases on the reactivity at an affordable computational cost. Details on the calculation of onset potentials and other energy-related descriptors can be found in the Supporting Information.…”