First-principles study of structural stability, elastic and dynamical properties of MnS

The norm-conserving pseudo-potentials method within the local spin density approximation are used to investigate the structural stability, Born effective charges, elastic and vibrational properties of three crystalline phases of manganese sulfide. Independent elastic coefficients and related polycrystalline quantities such as Poisson's ratio, shear modulus and Young's modulus which are estimated by using the Voigt-Reuss-Hill approximations have been computed. The elastic anisotropies in three phases are analyzed in detail using several methods. We calculate Born effective charges for MnS, which are found to be isotropic in three phases of MnS. The density of phonon states and full phonon dispersion curves of MnS are obtained using the direct method based on computed Hellmann-Feynman forces for the first time. The origin of the differences between acoustic and optical branches in the three phases of MnS are discussed and compared in detail. The Raman and infrared active phonon modes at the P-point are analyzed. The phonon dispersion results show that alpha-, beta- and gamma-MnS are dynamically stable. There is no experimental and theoretical data with regard to elastic constants, Born effective charges and vibrational modes, so the values that we have calculated may serve as predictions. (C) 2014 Elsevier B.V. All rights reserved.