Investigation of structural, electronic and dynamic properties of MnS by Ab-Initio method

In this dissertation, the structural, electronic, elastic properties, Born effective charges, phonon dispersion curves and the phonon density of states of manganese sulphide (alpha-MnS, beta-MnS and gamma-MnS phases) have been investigated by using the density functional theory and ab-initio pseudopotential method within the local spin density approximation. The calculated equilibrum lattice parameters are in the agreementwith the available experimental and theoretical results. alpha-MnS has an indirect band gap, whereas, beta-MnS and gamma-MnS have a direct band gap in the Brillouin zone. The elastic constants were derived using the ?Volume-conserving? technique. Born effective charges tensors for each ion, which determine the non-analytic contribution to the dynamical matrix in the limit q->0. The phonon dispersion curves for MnS of the three phases were derived using the ?finite differences? method. The LO/TO splitting was extracted from phonon frequencies found within the supercell. The phonon dispersion curves of some k-points give negative frequencies which indicates the beta-MnS and gamma-MnS structure are metastable. We have also made comparisons with related experimental and theoretical data which is available.