Phonon dynamics of neptunium chalcogenides

We have performed phonon calculations of Neptunium Chalcogenides (NpX) (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. The model predicts that the short range breathing phenomenon play a dominant role in the phonon properties. We also report, for the first time specific heat for these compounds.