  We have performed a first principles study of structural, mechanical,
electronic, and optical properties of orthorhombic Sb2S3 and Sb2Se3 compounds
using the density functional theory within the local density approximation. The
lattice parameters, bulk modulus, and its pressure derivatives of these
compounds have been obtained. The second-order elastic constants have been
calculated, and the other related quantities such as the Young's modulus, shear
modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye
temperature, and hardness have also been estimated in the present work. The
linear photon-energy dependent dielectric functions and some optical properties
such as the energy-loss function, the effective number of valance electrons and
the effective optical dielectric constant are calculated. Our structural
estimation and some other results are in agreement with the available
experimental and theoretical data.
