PHONON-DISPERSION RELATIONS OF METALLIC NISI2 AND COSI2 BY SEMIEMPIRICAL TIGHT-BINDING CALCULATION

We report some preliminary results concerning the phonon dispersion re lations and the density of states of NiSi2 and CoSi2 obtained with sem i-empirical tight-binding calculations. In the nickel disilicide case we obtain a good agreement to the experimental disorder-activated Rama n spectrum. For CoSi2 we point out that the independent behavior of th e acoustic dispersion relations with respect to the optical branches, formerly predicted on the basis of neutron scattering data, does not m atch with the low-frequency position of Raman and infrared modes, very recently observed and confirmed by ab-initio calculations.