First-principles calculations and tight-binding molecular dynamics simulations of the palladium-hydrogen system

Abstract

We present a study of palladium-hydrogen system by the linearized augmented plane-wave (LAPW) and Naval Research Laboratory (NRL) tight-binding (TB) methods. We constructed a TB Hamiltonian by fitting to first-principles LAPW data for the electronic energies of a large range of palladium and palladium hydride structures differing in symmetry and compositions as a function of volume. This TB Hamiltonian was then used to calculate phonon frequencies and elastic constants. Our calculations show good agreement with experiments and demonstrate the efficiency of the NRL-TB scheme. In addition, we performed tight-binding molecular dynamics simulations to calculate the density of states, mean-squared displacement, and the formation energy as a function of hydrogen content. We found a relative dip in the lattice energy of structures near the experimental limit of hydrogen content. We calculated the nearest hydrogen-hydrogen distance for various compositions of palladium hydride and confirmed the Switendick criterion.