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本文提出一种收敛的点电荷和Hartree-Fock表面势构成的自洽晶体场Madelung势用于原子簇量子化学从头计算。前者的计算类似于核吸引积分的单电子积分, 后者可以通过点群对称性操作从原子簇内的积分矩阵元得到。点电荷的大小和原子簇内对应的原子电荷相等, 其数目以晶体场势收敛为标准确定。介绍加速计算的程序技巧。该模型用于高温超导体YBa2Cu3O7的全电子从头计算并得到一些新结果。 相似文献
224.
本文采用自洽场分子轨道UHF/6-31G从头计算法, 辅以能量梯度法研究气相烯丙醇光异构化反应的机理。全部优化了T1态势能面上反应物、过渡态、中间体和产物的几何构型。基于Fukui提出的内禀反应坐标理论(IRC)计算这一体系的反应途径, 并针对各驻点进行MP2/6-31G的相关能校正, 得到该反应在激发态进行并为一经历双自由基中间体的分步反应的结论。支持了实验工作者提出的机理。 相似文献
225.
Jong Kwan Im Jin Chul Jung 《Journal of polymer science. Part A, Polymer chemistry》2000,38(3):402-410
AB‐type homo‐ and copoly(etherimide)s were prepared by the polymerization of 3‐ and 4‐(3,4‐dicarboxyphenyloxy)aniline hydrochlorides ( 3A and 4A ) at 160 °C in dimethylacetamide in the presence of triethylamine and triphenyl phosphite. After the structures of the polymers were characterized, their solubilities, ultraviolet–visible (UV–vis) absorption behaviors, thermal properties, and crystallinities were measured, and these properties are discussed with respect to the structure of the homopolymers and the composition of the copolymers. Poly(etherimide) (PEI) derived from 3A [PEI( 3A )] was amorphous and soluble in chloroform on heating, whereas that derived from 4A [PEI( 4A )] was crystalline and insoluble in common organic solvents even on heating. In UV–vis absorption spectra, PEI( 4A ) showed a small bathochromic shift relative to N‐phenylphthalimide, but PEI(3A) did not. PEI(3A) revealed a glass‐transition temperature (Tg) at 195 °C, but no Tg was detectable for PEI( 4A ). All the measured physical properties of the copoly(etherimide)s showed a good dependence on their composition between PEI( 3A ) and PEI( 4A ). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 402–410, 2000 相似文献
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X.‐Q. Wang D. Xu M.‐K. Lü D.‐R. Yuan G.‐H. Zhang F.‐Q. Meng S.‐Y. Guo M. Zhou 《Crystal Research and Technology》2001,36(1):73-84
Bimetallic thiocyanate complexes crystal materials belonging to ABTC structure type: ZnCd(SCN)4 and AHg(SCN)4 (A = Zn, Cd, Mn ) which are potentially useful in second harmonic generation (SHG) have been prepared. Their structural, optical and physicochemical properties are characterized by infrared spectroscopy, X‐ray powder diffraction, vis/UV/NIR spectroscopy, SHG measurements and thermal analysis. The states of crystal growth solutions are discussed in this article. The crystals belong to tetragonal system with the space group I‐4 and exhibit SHG efficiencies over one order of magnitude higher than that of Urea. Their transparency cutoffs lie in the UV region, and they possess good physicochemical stabilities. 相似文献
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Computer simulations of the step-growth homopolymerization of an AB2 monomer have been carried out on a square lattice. No rearrangements of units were made between reaction events. Instead, the capture radius, i.e., the maximum distance between the randomly selected unit and its reaction partner was changed. The reaction was considered as controlled either by diffusion and local concentration fluctuations or by the law of mass action (classical limit). The size distribution of polymer species and the extent of cyclization reactions in the polymerization are discussed. 相似文献