Mechanical stability of Pd-H systems: A molecular-dynamics study

Abstract

We use the Nose\ifmmode\acute\else\textasciiacute\fi{} and Rahman-Parrinello molecular-dynamics formalism to study the equilibrium structure and elastic properties of bulk Pd as a function of temperature and hydrogen concentration. Introducing tensile stress as an independent variable into this formalism enables us also to study the elastic breakdown and crack formation as a function of a uniaxially applied load. The calculations are performed using a model many-body alloy Hamiltonian based on ab initio density-functional results for Pd-H systems. Our results indicate that the microscopic origin of ``hydrogen embrittlement'' is an increased ductility and plasticity in regions saturated by hyrogen, in agreement with the postulated hydrogen-enhanced local-plasticity mechanism.