Lattice dynamical properties of neptunium chalcogenides

The phonon calculations of neptunium chalcogenides (N_pX; X = S, Se, Te) based on breathing shell model (BSM) which includes breathing motion of electron of the Np-atoms due to f-d hybridization, have been performed. The significance of this approach in predicting the phonon properties of N_pX compounds has been discussed and the role of f-electron has been examined. The model predicts that the short range breathing phenomenon plays a dominant role in the phonon properties. The specific heat for these compounds has been reported. (author)