摘要: Ab initio electronic structures for β-Ge_{3}N_{4} are investigated using ultrasoft pseudo-potential method within the generalized gradient approximation functional. The lattice parameters are predicted theoretically, and are compared with available experimental data and the other theoretical results. The elastic constants calculations reveal that the phenacite structure is a stable phase in the pressure range of 020GPa. The high bulk modulus (B=180.2GPa) indicates that β-Ge_{3}N_{4 }is a relatively hard material. β-Ge_{3}N_{4} has a direct band gap of 2.94eV, indicating its promising applications as a semiconductor in electronics and optical fibers. On the other hand, the density of states analysis is also included in this paper.* Corresponding author: CHEN Dong

作者: A. Chik, S. Saad, R.M. Zaki, F. Che Pa, C.K. Yeoh

摘要: The electronic structure of the perovskite manganites LaMnO_{3 } and La_{2/3} Al_{1/3} MnO_{3} was presented. The calculations were made within density functional theory (DFT) and PBE exchange correlations energy approximation. It was found that inclusion of Al dopants add additional states near the Fermi level and decreasing the resistivity values for all temperature range.

摘要: The structural and elastic properties of the cubic spinel Ge_{3}N_{4} semiconductor have been investigated using the ab initio scheme within the generalized gradient approximation in the framework of density functional theory. Quantities such as lattice constants and elastic constants of interest are calculated. A good agreement is found between our results and the other data. Through the lattice dynamics, in which the finite displacement method is used, we have obtained successfully the thermal properties such as the phonon curve, free energy, heat capacity and Debye temperature in the whole temperature range from 0 to 1000K. It is the authors ambition that these results will inspire further experimental study on the Ge-based semiconductors. * Corresponding author: CHEN Dong

摘要: We investigated the nucleation of SWNTs and the role of metallic catalyst using firstprinciples
calculations. To avoid dangling bonds a closed cap forms on a metal surface. 6 pentagonal
rings are introduced into the cap, which reduces the strain energy. A unique tube chirality then grows
from the cap, which is controlled by the metal lattice at the nucleation stage. We found that chirality
of nanotubes affects the bond energies, including dangling bonds, carbon-carbon bonds & carbonmetal
bonds.

摘要: Performing ab-initio total-energy calculations to investigate the adsorption and diffusion
processes of the Au atoms with both the clean Si(001)-(1×1) and H-terminated Si(001)-(2×1) surfaces. It
was found that, on the clean Si(001)-(1×1) surface, the most stable adsorption sites for Au atoms are
middle part of four Si atoms, while on H-terminated Si(001)-(2×1) surface, the most stable sites are the
middle part of a Si-Si dimer. The result showed that surface hydrogenation make most stable site transfer
and affect the adsorption of Au on Si(001) surface.

作者: Vsevolod I. Razumovskiy, A.Y. Lozovoi, Igor M. Razumovskii, Andrei V. Ruban

摘要: A new approach to the design of Ni-based polycrystalline superalloys is proposed. It is based on a concept that under given structural conditions, the performance of superalloys is determined by the strength of interatomic bonding both in the bulk and at grain boundaries of material. We characterize the former by the cohesive energy of the bulk alloy, whereas for the latter we employ the work of separation of a representative high angle grain boundary. On the basis of our first principle calculations we suggest Hf and Zr as “minor alloying additions” to Ni-based alloys. Re, on the other hand, appears to be of little importance in polycrystalline alloys.

摘要: The vacancy properties in group-IV hexagonal close-packed metals (Ti, Zr and
Hf) have been investigated by Density Functional Theory (DFT) calculations performed with
the SIESTA code. The migration energies are found to be systematically lower by »0.15 eV
within the basal plane than out of the basal plane. The electronic origin of this significant
contribution to diffusion anisotropy is evidenced by the analysis of the local electronic densities
of states and by a comparison with and empirical potential. The average value of the migra-
tion energy is in very good agreement with available experimental data in Zr. The activation
energies for self-diffusion obtained assuming a vacancy mechanism are in good agreement with
experiments in Zr and Hf, although slightly too small, but a significant discrepancy is observed
in Ti.