  We have performed a first principles study of structural, mechanical,
electronic, and optical properties of orthorhombic Sb2S3 and Sb2Se3 compounds.
The calculations have been carried out within the local density approximation
using norm conserving pseudopotentials. The lattice parameters, bulk modulus,
and its pressure derivatives of the 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 and Debye temperature 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.
