Papers by Keyword: Ab Initio

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Authors: Chao Xu, Dong Chen
Abstract: Ab initio electronic structures for β-Ge3N4 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-Ge3N4 is a relatively hard material. β-Ge3N4 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
Authors: A. Chik, S. Saad, R.M. Zaki, F. Che Pa, C.K. Yeoh
Abstract: The electronic structure of the perovskite manganites LaMnO3 and La2/3 Al1/3 MnO3 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.
Authors: Chao Xu, Dong Chen
Abstract: The structural and elastic properties of the cubic spinel Ge3N4 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
Authors: Jordi Rius, Xavier Torrelles, Carles Miravitlles
Authors: L. Li, S. Reich, J. Robertson
Abstract: 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.
Authors: Tokuteru Uesugi, Masanori Kohyama, Masahide Kohzu, Kenji Higashi
Authors: Wei Wei Ju, Tong Wei Li, Jing Han You, Zheng Xin Tang, Xiao Yang Gong, Hui Wang, Zhi Qiang Zhen, Qing Guo Zhang
Abstract: 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.
Authors: Vsevolod I. Razumovskiy, A.Y. Lozovoi, Igor M. Razumovskii, Andrei V. Ruban
Abstract: 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.
Authors: Guillaume Vérité, F. Willaime, Chu Chun Fu
Abstract: 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.
Authors: F. Sahtout Karoui, A. Karoui, George A. Rozgonyi, M. Hourai, Koji Sueoka
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