  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 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.
MD simulations of the nonlinear dynamics of Ni and Nb confirmed that high
frequency ILMs may exist in these metals.
