Exciting discrete breathers of two types in a computer 3D model of Pt$_3$Al crystal

The possibility of exciting discrete breathers (DBs) with both soft and hard nonlinearity in a threedimensional crystal has been shown for the first time using molecular dynamics simulation by example of an ordered Pt$_3$Al crystal model. The oscillation frequencies of DBs of the first (soft) type fall in the gap of the phonon spectrum and decrease with increasing amplitude. For DBs of the second type, the oscillation frequencies are above the phonon spectrum and increase with the amplitude, i.e., exhibit hard nonlinearity. An example of the transformation of a hard DB into a set of gap (soft) DBs with soft nonlinearity is presented. The influence of various factors on the lifetime of interacting DBs is considered.