Molecular dynamics simulations of discrete breathers in the nickel hydride

Computational assessment of the discrete breathers, i.e. spatially localized and periodic in time nonlinear excitations in crystals, is performed in nickel hydride with an even stoichiometry by means of molecular dynamics simulations. The breathers consisting of hydrogen and metallic atoms were excited following the experience obtained earlier by modelling the breathers in pure metallic systems. Stable breathers were found in the nickel hydride system for the hydrogen atoms oscillating along <100> and <111> polarization axes. Two types of the stable breathers involving single oscillating hydrogen and a pair of hydrogen atoms beating in antiphase mode were discovered. Analysis of the breather characteristics reveals that its frequency is in the phonon gap or lying in the optical phonon band of phonon spectrum near the upper boundary. Analysis of the movement of atoms constituting the breather was performed to understand the mechanism that enables the breather stabilization and long-term oscillation without dissipation its energy to the surrounding atoms. Thus, our analysis provides an explanation for the existence of the long-living stable breathers in nickel hydride.