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991.
The clusters of Fe, Ni, and Fe–Ni are investigated computationally using a density functional approach. The geometries of clusters are optimized under the constraint of well-defined point group symmetries at the UB3LYP/LanL2DZ level. The equilibrium geometries and binding energies are presented and discussed, together with natural populations and natural electron configurations. In addition, the binding energies of Fen−xNix clusters are found to generally decrease by successive substitutions of Ni atoms for Fe atoms. For Fen−xNix clusters, the comparisons on total energies between isomers indicate that Ni atoms energetically prefer clustering in the mixed Fe–Ni clusters. The calculations for Fen−xNix clusters show that the clustering leads to a segregation of Ni atoms from Fe atoms. 相似文献
992.
Xin Xu Chao Cai Luyuan Hao Yachong Wang Qunxiang Li 《Materials Chemistry and Physics》2009,118(2-3):270-272
Cerium-doped Lu4Si2O7N2 green phosphors were synthesized by a high-temperature solid-state reaction method under nitrogen atmosphere. Compared with Ce-doped Y4Si2O7N2 phosphors, Ce-doped Lu4Si2O7N2 phosphors showed longer wavelengths of both excitation and emission, lower Stokes shift, and much stronger emission intensity. Based on the first-principles calculations of the two phosphors, the strong emission intensity originates from the large density of states. At last, the effects of Ce3+ concentration on photoluminescence were also examined. 相似文献
993.
Corrosion inhibition of mild steel in molar perchloric acid by 3,5-bis(n-pyridyl)-4-amino-1,2,4-triazoles (n-PAT, n = 2, 3 and 4) was studied at 30 °C using gravimetric and electrochemical impedance spectroscopy techniques. Protection efficiencies of 95% and 92% were obtained with 12 × 10−4 M of 3-PAT and 4-PAT, respectively; while 2-PAT reached only 65%. The inhibiting properties of n-PAT were found to depend on the concentration and the order of increasing inhibition efficiency was correlated with the modification of the position of the nitrogen atom in the pyridinium substituent. It was shown that adsorption of 4-aminotriazole derivatives on the steel surface is consistent with the Langmuir adsorption isotherm and the obtained standard free energy of adsorption () values indicate that the corrosion inhibition of the mild steel in 1 M HClO4 is depends on both physic-and chemisorption. A significant correlation is obtained between inhibition efficiency and quantum chemical parameters using semi-empirical quantitative structure-activity relationships (QSAR) approach. 相似文献
994.
A series of well-defined poly[2,7-(9,9-dihexylfluorenyl)-co-bipyridinyl] [F-(BPY)x] with varied BPY (bipyridine) unit contents from 0 to 50% were synthesized using palladium(0) catalyzed Suzuki cross-coupling reactions, and well characterized using 1H NMR, IR, and GPC. Their photophysical and electrochemical properties were investigated. These copolymers showed pure blue photoluminescence (440 nm) in dilute solutions with the fluorescence quantum yield >0.6. Electron-affinity potentials (LUMO levels) of these polymers estimated from cyclic voltammetry were significantly decreased with the increase of BPY content in the polymer backbone, and a level of 2.43 eV for alternating BPY-fluorene polymer (50% BPY) was achieved, making them good candidates for electron injection and transport materials in EL devices. A further great decrease in LUMO level up to 2.99 eV was found when Zn2+ was chelated into polymers. The experimental observations were supported by the quantum chemical calculations on these polymers, which provided the proof for the intuitive notion of an intramolecular charge transfer band in polymer chain. 相似文献
995.
996.
This work focuses on the use of computational Grids for processing the large set of jobs arising in parameter sweep applications. In particular, we tackle the mapping of molecular potential energy hypersurfaces. For computationally intensive parameter sweep problems, performance models are developed to compare the parallel computation in a multiprocessor system with the computation on an Internet‐based Grid of computers. We find that the relative performance of the Grid approach increases with the number of processors, being independent of the number of jobs. The experimental data, obtained using electronic structure calculations, fit the proposed performance expressions accurately. To automate the mapping of potential energy hypersurfaces, an application based on GRID superscalar is developed. It is tested on the prototypical case of the internal dynamics of acetone. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
997.
为提高掘进机截割头的焊接质量和生产率,设计开发了数控变位机应用于焊接工艺过程中。针对截割头的参数和其复杂结构的焊接,给出了数控变位机机械部分的设计方法与计算过程,为设计和应用数控变位机于掘进机零件的制造提供参考。 相似文献
998.
We have performed first principles total energy calculations to investigate the deposit of yttrium digermanide on the Si(111) surface. We have used the periodic density functional theory as implemented in the Quantum-ESPRESSO package. For the adsorption of a monolayer of yttrium digermanide on the Si(111)-(1 × 1) surface, we have found that the most stable geometry corresponds to a configuration with Y atoms occupying the T4 site above a second layer Si atom, and with a Ge bilayer on top of the structure. The atomic structure of the Ge bilayer is similar to that of Si (Ge) in the bulk but rotated 180° with respect to the crystal. For the three dimensional growth of a few layers of yttrium digermanide on Si(111) we have considered a hexagonal structure with (√3 × √3) periodicity, similar to the one found in the growth of few layers of YSi2 on Si(111): graphite-like Ge planes (with vacancies) intercalated with yttrium planes. As in the case of a single layer of YGe2, there is a formation of a Ge bilayer on top of the structure. In this case, the Gedown atoms of the bilayer, which are on top the vacancies, move down towards the vacancy, while Ge atoms in the graphitic layer, which are below the Geup atoms of the bilayer, are displaced towards the vacancy. 相似文献
999.
Shude Ji )? Liguo Zhang ) Xuesong Liu ) Jianguo Yang ) ) School of Aerospace Engineering Shenyang Institute of Aeronautical Engineering Shenyang China ) State Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin China 《材料科学技术学报》2009,(6)
On basis of the similitude principles, the conception of virtual simulative component and the auxiliary value of welding residual stress, which is deduced by the welding conduction theory, the relation of the welding residual stress between the simulative component and the practical component was attained. In order to verify the correctness of the relation, the investigation was done from the view of the welding experiment and the numerical simulation about the simulative component and the practical compone... 相似文献
1000.
The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H2 molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab initio density functional theory investigation of H2 dissociation and subsequent atomic H diffusion on TM (= Ti, V, Zr, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-doped Mg(0001) surfaces. The calculations show that doping the surface with TMs on the left of the periodic table eliminates the barrier for the dissociation of the molecule, but the H atoms bind very strongly to the TM, therefore hindering diffusion. Conversely, TMs on the right of the periodic table do not bind H, however, they do not reduce the barrier to dissociate H2 significantly. Our results show that Fe, Ni and Rh, and to some extent Co and Pd, are all exceptions, combining low activation barriers for both processes, with Ni being the best possible choice. 相似文献