COSMIC(90): An improved molecular mechanics treatment of hydrocarbons and conjugated systems

Summary Four modifications to the COSMIC molecular mechanics force field are described, which greatly increase both its versatility and the accuracy of calculated conformational energies. The Hill non-bonded van der Waals potential function has been replaced by a two-parameter Morse curve and a new H-H potential, similar to that in MM3, incorporated. Hydrocarbon energies in particular are much improved.A simple iterative Hückel pi-electron molecular orbital calculation allows modelling of conjugated systems. Calculated bond lengths and rotational barriers for a series of conjugated hydrocarbons and nitrogen heterocycles are shown to be as accurate as those determined by the MM2 SCF method.Explicit hydrogen-bonding potentials for H-bond acceptor-donor atom pairs have been included to give better hydrogen bond energies and lengths. The van der Waals radii of protonic hydrogens are reduced to 0.5 Å and the energy well depth is increased to 1.0 kcal mol^-1.Two new general atom types, N⁺ _sp ² and O^- _sp ³ , have been introduced which allow a wide variety of charged conjugated systems to be studied. A minimum of parameterisation is required, as the new types are easily included in the Hückel scheme which automatically adjusts bond and torsional parameters according to the defined bond-order relationships.     

桥式起重机水平刚架结构的设计计算

为桥式起重机金属结构设计中,全面、准确地考虑水平载荷的影响,本文介绍了桥式起重机在惯性力、风力、偏斜侧向力作用下,水平刚架结构的计算简图和准确、简单的内力计算式。方便了设计,提高了计算精度,可供设计选用。     

Ab initio study on structure and phase transition of A- and B-type rare-earth sesquioxides Ln2O3 (Ln=La-Lu, Y, and Sc) based on density function theory

Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln₂O₃ (where Ln=La-Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A- and B-type rare-earth sesquioxides Ln₂O₃. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln₂O₃ reflect the so-called “lanthanide contraction”. With the increase of the Ln³⁺-cation radius, the bulk modulus of Ln₂O₃ decreases and the polymorphic structures show a degenerative tendency.     

树状管网技术经济计算分析

通过对目标函数(年费用折算值)W0在水力约束条件下最小值的分析计算,介绍了起点水压未知树状管网技术经济计算的方法,并求出了相应的经济水头损失hij和经济管径Dij的表达式。     

Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B1∏ of 7LiH

The reasonable dissociation limit of the second excited singlet state B¹∏ of ⁷LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B¹\Pi state are calculated using a symmetry-adapted-cluster configuration--interaction method in full active space. The whole potential energy curve for the B¹∏ state is obtained over the internuclear distance ranging from about 0.10nm to 0.54nm, and has a least-square fit to the analytic Murrell--Sorbie function form. The vertical excitation energy is calculated from the ground state to the B¹∏ state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B¹∏ state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.     

会计的发展趋势

论述了在知识经济条件下，会计工作的重要地位及发展趋势，即会计核算向多方面、高质量、全方位、知识管理、综合化、边缘化等方向发展，对拓展会计工作的内涵和外延、满足现代企业管理有重要的现实意义。     

杨庄煤矿塌陷湖水资源勘查计算

通过对塌陷湖的实地勘查,运用水均衡原理,计算出该湖可供开采的水资源,认为该塌陷湖可作为淮北市供水后备水源地之一。     

配电网结线变化时电压损失和功率损耗的矩阵算法

作者在文献[1]中,曾提出用关联矩阵法计算配网参数,以监察其供电质量和经济指标,本文则提出当电网负荷结点增加或结线图改变时,由计算机自动修改原配网关联矩阵并求得新配网的电压损失和功率损耗值的方法。     

[Co(2,3-tri)(ibn)Cl][ZnCl4]体系一经式异构体的晶体结构及体系异构体的理论计算研究

用单晶X-射线衍射分析方法解析了[Co(2,3-tri)(ibn)Cl]²⁺(2,3-tri=N-(2-氨基乙基)-1,3-丙二胺,ibn=1,2-二氨基-2-甲基丙烷)体系中一经式异构体(m2-[Co(2,3-tri)(ibn)Cl][ZnCl₄])。该晶体属单斜晶系,空间群P2₁/c,a=11.317(3)?,b=14.931(4)?,c=11.646(3)?,β=1     

Synthesis on the basis of electrogenerated carbenes

A series ofS _N2 reactions with halomethanes as substrates and the corresponding anions as nucleophiles were studied by the semiempirical MNDO and AM1 methods, taking into account solvent effects. Analysis of the kinetics, structures of reagents, intermediates and products, and charge distribution in them allows one to draw the conclusion that the retardation ofS _N2 reactions is stronger in solvents than in the gas phase, and the rates of reactions involving anions with a lower number of halogen atoms are higher.For Part 8 see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2148–2154, November, 1995.This work was partially financially supported by the International Science Foundation (Grant No. MHYOO).