Threshold behavior of strongly localized nonlinear modes in crystals with Fermi resonance interaction

We report the existence of strongly localized modes in thin films and cryst als with Fermi resonance interaction between vibration modes of molecules. Several families of bright and dark localized modes are investigated theore tically in two- and three-dimensional systems. Simple theoretical estimatio ns are confirmed by numerical calculations. It is shown that in higher dime nsions the solutions exist which do not have their one-dimensional analogs. The strongly localized Fermi resonance modes demonstrate the threshold beh avior in any dimension in contrast to the nonlinear lattices with cubic int eraction between sites.