Showing papers by "Xiang-Feng Zhou published in 2006"

First-principles study of electronic structure and optical properties of heterodiamond BC 2 N

Abstract: Heterodiamond ${\mathrm{BC}}_{2}\mathrm{N}$, as a kind of superhard material expectable, is studied using the ab initio pseudopotential density functional method. All the calculations are performed after geometric optimization starting from an eight-atom zinc-blende structure unit cell. For all the structures possible, we calculate in detail the structural parameters, charge transfers, bond populations, band structures, density of states, and optical properties (dielectric function, refractive index, absorption coefficient, reflectivity, electron energy loss spectrum, and photoconductivity). In addition, the optical anisotropy of some structures is also discussed. Our calculated results show that all the structures are metastable and some of them tend to form graphitelike structures and exhibit semimetallic behavior leading to interesting optical properties.

Chalcopyrite polymorph for superhard BC2N

Abstract: A chalcopyrite structure is predicted for the potential superhard boron-carbonitride (BC2N), based on ab initio pseudopotential density functional method. Lattice constant, formation energy, bulk modulus, band structure, and electron density of states are calculated. The results show that this compound is a wide gap semiconductor with a direct band gap of about 3.3eV. The calculated Vickers hardness is about 72GPa, which is very close to the measured hardness of c-BC2N (76±4GPa).

Infrared and Raman spectra of β − B C 2 N from first principles calculations

Abstract: We present the study on the infrared and nonresonant Raman spectra of $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{B}{\mathrm{C}}_{2}\mathrm{N}$ within the framework of ab initio pseudopotential density functional perturbation theory in a four-atom orthorhombic unit cell. The Raman tensors are calculated from the second-order response of the electronic density matrix with respect to a uniform electric field. Comparison between experiments and calculations for cubic BN is presented to test our method in reproducing all the measured features quantitatively. The LO/TO splitting is well imposed by adding the nonanalytical part deduced from the Born effective charge and macroscopic dielectric constant. Finally, different Raman experiment configurations for $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{B}{\mathrm{C}}_{2}\mathrm{N}$ are discussed.