检索结果-南通市图书馆

Study on the construction of satisfactory nonorthogonal localized molecular orbitals

在线全文

学校读者我要写书评

暂无评论

Science China Chemistry 2004年第1期47卷 1-9页

作者： FENG Huasheng BIAN Jiang LI Lemin State Key Laboratory of Rare Earth Materials and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China State Key Laboratory of Rare Earth Materials and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China State Key Laboratory of Rare Earth Materials and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China

Comparing to orthogonal localized molecular orbitals (OLMO), the nonorthogonal localized molecular orbitals (NOLMO) exhibit bonding pictures more accordant with those in the traditional chemistry. They are more contracted, so that they have a better transferability and better performances for the calculation of election correlation energies and for the linear scaling algorithms of large systems. The satisfactory NOLMOs should be as contracted as possible while their shapes and spatial distribution keep in accordance with the traditional chemical bonding picture. It is found that the spread of NOLMOs is a monotonic decreasing function of their orthogonality, and it may reduce to any extent as the orthogonality descends. However, when the orthogonality descends to some point, the shapes and spatial distribution of the NOLMOs deviate drastically from the traditional chemical bonding picture, and finally the NOLMOs tend to linear dependence. Without the requirement of orthogonalization, some other constraints have to be imposed for constructing satisfactory NOLMOs by minimizing their spread functional. It is shown that satisfactory results can be generated by coupling the minimization of orbital spread functionals with the maximization of the distances between orbital centroids.

关键词： quantum chemical calculation, chemical bonding, nonorthogonal localized molecular orbital, orbital spread.

Structure stability and configuration evolution of Al_n(n=3, 4, 6, 13, 19) clusters

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2006年第4期49卷 385-392页

作者： PENG Ping LI Guifa ZHENG Caixing HAN Shaochang LIU Rangsu School of Materials Science and Engineering Hunan University Changsha 410082 China School of Materials Science and Engineering Hunan University Changsha 410082 China School of Materials Science and Engineering Hunan University Changsha 410082 China School of Materials Science and Engineering Hunan University Changsha 410082 China School of Materials Science and Engineering Hunan University Changsha 410082 China

Using a first-principles pseudo-potential plane wave method, the geometrical and electronic structures of Aln (n=3, 4, 6, 13, 19) clusters with different configurations have been calculated. Several parameters such as the binding energy Eb and the HOMO-LUMO energy gap ?EH-L have been adopted to characterize and analyze the structure stability of these clusters, and their configuration evolutions are also investigated by linear synchronous transit (LST) method. It is demonstrated that the stable configura- tions of Al3, Al4, Al6, Al13, Al19 clusters are triangle, rhombus, octahedron, icosahedron and double icosahedron, respectively. For Al6 and Al19 clusters there are metastable structures of parallelogram and octahedron, respectively, whereas in the Al3, Al4 and Al13 clusters, no metastable configuration is validated. There exist a large energy gap and a low energy barrier between the octahedron and the parallelogram of the Al6 cluster, so the transfor- mation from its metastable to stable structures is rather easy. By contrast, a small energy gap and a high energy barrier between the stable and metastable structures of Al19 cluster mean its configuration evolution from the octahedron to the double icosahedron occurs hardly, therefore the metastable octahedron configuration of Al19 cluster can be extensively detected in experiments and simulations.

关键词： first-principles calculation, Al cluster, configuration evolution.

Density functional calculations of large systems containing heavy elements by means of the regionalization algorithm

在线全文

学校读者我要写书评

暂无评论

Science China Chemistry 2004年第6期47卷 453-465页

作者： HU Xiangqian LI Lemin State Key Laboratory of Rare Earth Materials and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China State Key Laboratory of Rare Earth Materials and Applications College of Chemistry and Molecular Engineering Peking University Beijing 100871 China

The regionalized computational method is extended to the non-relativistic, scalar and 2-component relativistic density functional calculation of large systems containing transition series or heavy main-group metal elements. A large system is divided into several regions which can be considered as relatively independent quantum mechanical subsystems. Taking into ac- count the Coulomb and exchange-correlation potentials as well as the Pauli repulsion exerted by the other subsystems, the Kohn-Sham equation related to subsystem K can be written as: (FK + FP )CK = SKCKεK K = A, B, C, L, K where FK , CK , SK , εK are the Fock matrix, the matrix of combination coefficients of orbitals, the overlap matrix of basis sets and the energy eigenvalue matrix, respectively. The matrix Fp K reflects the Pauli repulsion from the other subsystems. FK may be non-relativistic, scalar or 2-component relativistic Fock matrix determined by the theoretical method related to the density functional calculations. The other matrices are mated with FK . Solving the Kohn-Sham equation for every subsystem and combining the results from the subsystem calculations, the electronic structural information of the whole system is derived. The density functional calculation of several molecules containing transition metal Ni or heavy main-group metal Tl or Bi is performed by the afore-mentioned regionalization algorithm. The obtained results for each molecule are compared with those from the density functional calculation of that molecule in its entirety in order to check the feasibility of the regionalization algorithm. It is found that with sufficiently large regional basis set in the subsystem calculation the accuracy of the results calculated by the regionalization al- gorithm is essentially the same as that from the calculation of the molecule in its entirety. With proper smaller regional basis sets the accuracy of the results calculated with the regionalization algorithm can still match the actual a

关键词： density functional calculation, large system, transition metal, heavy element, regionalization algorithm.

Three-dimensional configurations of organic/inorganic hybrid nanostructural blocks (I).A quantum mechanical investigation for ladder-like structure of vinylsilsesquioxane

在线全文

学校读者我要写书评

暂无评论

Science China Chemistry 2004年第5期47卷 388-395页

作者： ZHANG Xingwen1,2, HU Lijiang1, HUANG Yudong1, SUN Dezhi2 & SUN Yi3 1. Department of Applied Chemistry,Harbin Institute of Technology, HUANG Yudong, Harbin 150001, China 2. Department of Environmental Engineering, Harbin Institute of Technology, Harbin 150001, China 3. Department of Experimental Mechanics,Harbin Institute of Technology, Harbin 150001, China Dept. of Applied Chem. Harbin Inst. of Technol. Harbin 150001 China Dept. of Environ. Eng. Harbin Inst. of Technol. Harbin 150001 China Dept. of Experimental Mech. Harbin Inst. of Technol. Harbin 150001 China

The organic/inorganic hybrid nanostructural vinylsilsesquioxanes (VSSO) were prepared from the hydrolytic condensation of vinyltrimethoxysilane (VMS). The proposed formu- las of VSSO were assigned with standard spectroscopic techniques, FTIR, NMR (1H, C and 13 29Si) and MALDI-TOF MS, and a generic formula of the SSO, Tn(OH)x(OR’)y(x, y = 0, 1, 2…; n = 1, 2…; T = RSiO1.5 ?(x+y)/2n). Geometric parameters (Si-O and Si-C bond lengths, Si-O-Si and O-Si-O bond angles) and total energies of the multi-structures of VSSO were calculated by a quantum mechanical investigation and molecular symmetries. According to the results of the calculation, most molecules had stabler ladder structures than the cage isomers, therefore, the most probably reasonable and optimum structure of the VSSO system was the ladder type.

关键词： vinyltrimethoxysilane (VMS), silsesquioxanes (SSO), sol-gel process, quantum mechanical calculation, MNDO.

High-order accurate dissipative weighted compact nonlinear schemes

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2002年第3期45卷 356-370页

作者：邓小刚 China Aerodynamics R. and D. Center Mianyang 621000 China

Based on the method deriving dissipative compact linear schemes (DCS), novel high-order dissipative weighted compact nonlinear schemes (DWCNS) are developed. By Fourier analysis,the dissipative and dispersive features of DWCNS are discussed. In view of the modified wave number, the DWCNS are equivalent to the fifth-order upwind biased explicit schemes in smooth regions and the interpolations at cell-edges dominate the accuracy of DWCNS. Boundary and near boundary schemes are developed and the asymptotic stabilities of DWCNS on both uniform and stretching grids are analyzed. The multi-dimensional implementations for Euler and Navier-Stokes equations are discussed. Several numerical inviscid and viscous results are given which show the good performances of the DWCNS for discontinuities capturing, high accuracy for boundary layer resolutions, good convergent rates (the root-mean-square of residuals approaching machine zero for solutions with strong shocks) and especially the damping effect on the spudous oscillations which were found in the solutions obtained by TVD and ENO schemes.

关键词： numerical calculation, compact schemes, nonlinear schemes, Euler equations, Navier-Stokes equa-tions.

New Approach to the Power Selection for Asynchronous Motor

在线全文

学校读者我要写书评

暂无评论

Journal of Donghua University(English Edition) 2001年第2期18卷 133-139页

作者：高建华胡洪国杨汝清 Research Institute of Robotics Shanghai Jiao Tong University Shanghai 200030

The heating calculation of three-phase squirrel- cage asynchronous motor on the condition of starting for a prescribed rotary angle is firstly studied with time dissection method and its corresponding algorithm is provided. Then based upon the algorithm, a new method for motor power selection is established. Motor initial power determined by load power ischecked and modified in terms of time crit erion, heating criterion,and starting torque *** appropriate motor power which meets three criterions is obtained at last, in the meantime, working displacement matrix andfrequency matrix used for control are acquired. Lifting motor of MDJ1800 low-level high- speed palletizer is taken as a reaI case in the paper.

关键词： time dissection, heating calculation, frequent starting,power selection, three-phase squirrel-cage asynchronous motor