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.we submit our manuscript " First principles prediction of the elastic, electronic, and optical properties of Sb 2 S 3 and Sb 2 Se 3 compounds". This manuscript is original and has not been published elsewhere and their intent is to publish in the Solid State Sciences. Cover LetterDear Editor, Thank you for your useful comments and suggestions on the language and structure of our manuscript. We have modified the manuscript accordingly, and detailed corrections are listed below point by point: 1) Please improve the clarity of letters used in figures 1 and 4. the clarity of letters used in figures 1 and 4 have been improved.2. Graphical abstract should be provided with figure only; the use of text will be allowed only when there is no alternative.  Graphical abstract have been provided with figure only.3.The tel/fax numbers (with country and area code)of the corresponding author should be provided on the first page of the manuscript.  On the first page of the manuscript have been provided the tel/fax numbers of the corresponding author.4. Page should be numbered consecutively.  Page have been numbered. Responses to Technical Check Results *Graphical Abstract

The structural, mechanical, electronic, and optical properties of orthorhombic Bi 2 S 3 and Bi 2 Se 3 compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some nonlinearities for Bi 2 S 3 and Bi 2 Se 3 (tensors of elasto-optical coefficients) under pressure.

No abstract

No abstract

No abstract

No abstract

The electronic energy band structure and linear optical properties of the ferroelectric semiconductor SbSI in the paraelectric phase are calculated by an ab initio pseudopotential method using density functional theory in the local density approximation. The calculated electronic band structure shows that SbSI has an indirect band gap of 1.45 eV and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV). The total density of states has been analysed. The linear energy dependent dielectric functions and some optical constants such as the absorption coefficient, extinction coefficient, refractive index, energy-loss function, reflectivity and optical conductivity, including self-energy effects, are calculated. The effective number of valence electrons and the effective optical dielectric constant are also calculated.

Cataloged from PDF version of article.The electronic structures of KNbO(3)were calculated within the density functional theory, and their evolution was analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phase. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared the results with the theoretical spectra calculated within Density Functional Theory. The dominant role of the NbO(6)octahedra in the formation of the energy spectra of KNbO(3)compound was demonstrated. The anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition