It is found that in some metals, an intrinsic localized mode may exist with frequency above the top of the phonon spectrum. The necessary condition, requiring a sufficiently high ratio of quartic to cubic anharmonicity, may be fulfilled because of screening of the interaction between ions by free electrons. Starting from the known literature values of the pair potentials, we have found that in Ni and Nb the derived localized mode condition is fulfilled. Molecular-dynamics simulations of the nonlinear dynamics of Ni and Nb confirmed that high-frequency intrinsic localized modes may exist in these metals.

• Received 21 March 2011

DOI:https://doi.org/10.1103/PhysRevB.84.144303