  Metal Chalcogenides have been known for important technological applications
and have attracted continuous interest in their structure, electronic, thermal
and transport properties. Here we present first principles calculations of the
vibrational and thermodynamic properties of NiX (X = S, Se, Te) compounds along
with inelastic neutron scattering measurements of the phonon spectrum in NiSe.
The measured phonon spectrum is in very good agreement with the computed
result. We also report the measurement of thermal expansion behavior of NiSe
using X-ray diffraction from 13 K to 300 K. The change in the hexagonal c
lattice parameter in NiSe is considerably greater as compared to a parameter.
The ab-initio calculated anisotropic Gr\"uneisen parameters of the different
phonon modes in all the chalcogenides along with the elastic constants are used
to compute anisotropic thermal expansion behviour, which is found in good
agreement with experiments. The displacement pattern of phonons indicate that
difference in amplitudes of Ni and X atoms follow the anisotropy of thermal
expansion behavior along c- and a-axis.
