CONNECTION BETWEEN THE TRUE VIBRATIONAL DENSITY-OF-STATES AND THAT DERIVED FROM INELASTIC NEUTRON-SCATTERING

The correction function connecting the true vibrational density of sta tes with that measured in inelastic neutron experiments is defined. Us e of this function is essential for multicomponent systems containing elements characterized by rather different scattering lengths or masse s. The correction function, calculated for a particular model system ( vitreous silica) constructed using molecular dynamics, is shown to be of the order of unity in this case. In the evaluation of the correctio n function, it has been found that the coherent contribution is neglig ible and so the incoherent approximation can be successfully applied. The frequency dependence of the correction function arises mainly from that of the partial vibrational density of states. A comparison of th e true vibrational density of states with the effective one obtained f rom an analysis of the dynamical structure factor is presented.