Multi-component delocalized nonlinear vibrational modes in nickel

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Delocalized nonlinear vibrational modes (DNVMs) are relatively new dynamical objects that can be used for testing interatomic potentials and for classification and finding new types of discrete breathers. In this work, for the first time, multi-component DNVMs in a single crystal of fcc nickel are studied using molecular dynamics method. Previously discovered two one-component DNVMs are used to construct and investigate properties of all possible two- and three-component superpositions. A quasi-periodic energy exchange between components in multi-component DNVMs is described. If the amplitudes of the one-component DNVMs in a superposition differ by less than four times, then an equivalent energy exchange between them is observed. Otherwise, an unequal energy exchange takes place, i.e. when the high-amplitude component gives up only a part of its energy leading to a slight increase in the amplitude of another component. The DNVMs consisting of two- and three-components have a lifetime of more than 10 ps as long as the initial atomic amplitudes do not exceed 0.08 Å. An increase in the initial amplitude leads to a substantial decrease in the lifetime due to the rapidly developing modulational instability. Some superpositions of modes with the same initial amplitudes of the components can transform into a one-component DNVM, while others remain multi-component ones. The results obtained in this work demonstrate the existence of multi-component DNVMs, being a superposition of two or three components, which significantly expands our understanding of their dynamics in an fcc lattice.