STOCHASTIC APPROACH TO SIMULATION OF LATTICE-VIBRATIONS IN STRONGLY ANHARMONIC CRYSTALS - ANOMALOUS FREQUENCY-DEPENDENCE OF THE DYNAMIC STRUCTURE FACTOR

A simple model describing the dynamics of a collective strongly anharm onic mode embedded in a thermostat is investigated by numerical integr ation of the Langevin equation using methods with strong and weak conv ergences. We apply ab initio potentials with several wells describing some types of such modes in the bce phase of Zr. The results obtained demonstrate a number of peculiarities of lattice vibrations, which do not keep within the limits of the conventional phonon picture. in part icular, an analysis of the results allows one to explain some unusual features of the lattice dynamics of Ti and Zr and their alloys (for ex ample, symmetrically forbidden splitting of phonon branches, central p eak).