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排序方式: 共有69条查询结果,搜索用时 31 毫秒
31.
Rodney J. Bartlett Josh Mcclellan J. C. Greer Scott Monaghan 《Journal of Computer-Aided Materials Design》2006,13(1-3):89-109
Quantum mechancial forces at the core of multi-scale simulations, require a one-electron Hamiltonian approach whose solution provide electronic energies, forces, and properties for > 1,000 atoms fast enough that it can drive large scale molecular dynamics. Such a transfer-Hamiltonian is hoped to be as predictive as accurate, ab initio quantum chemistry for such systems. To design the Hamiltonian requires that, we investigate rigorous one-particle theories including density functional theory (DFT) and the recently proposed, correlated orbital potential (COP) approach that has been developed solely from wavefunction considerations. The latter insists upon exact, principal ionization potentials and electron affinities for a system, while DFT insists upon the exact density and the HOMO ionization. These two complementary approaches help identify the essential quantities that an exact one-particle theory of electronic structure requires. The intent, then, is to incorporate these into a simple approximation that can provide the accuracy required but at a speed four orders of magnitude faster than today’s DFT. The theory is presented and its neglect of diatomic differential overlap (NDDO) realization is illustrated for select systems. 相似文献
32.
Semi-empirical simulation of Zn/Cd binding site preference in the metal binding domains of mammalian metallothionein 总被引:1,自引:0,他引:1
Metallothionein, a two-domain protein, naturally binds sevengram atoms of divalent ions such as Zn and Cd. Four of the metals(Ml, M5, M6 and M7) are found in the -domain and three (M2,M3 and M4) in the ß-domain. Previous studies haveshown that metals in the -domain are more readily exchangeable,and the level of avidity is site specific. By semi-empiricalMNDO modified neglect of diatomic overlap calculations, we foundthe tendency of binding energy for Cd to be M3 > M2 >M4 in the ß-cluster and M5 > M7 > Ml, M6 inthe -cluster. Thus, the replacement of Zn by Cd can be expectedto follow the order M4 M2 M3 in the ß-domain andMS M7 M1 or M6 in the -domain. This is reflected by energydifferences computed with a series of simulated structures derivedfrom either X-ray crystallography or NMR coordinates. 相似文献
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蔗糖甜度与分子上的8个羟基密切相关,使用亲油性卤原子,取代蔗糖分子的葡糖基和果糖基上特殊位置的羟基,可以使蔗糖甜味明显增强,这些特殊位置包括C-4、C-1'、C-4'和C-6'。用化学软件Hyperchem7.5,采用PM3半经验量子化学方法计算了16个蔗糖卤代衍生物的5种量子化学结构参数,取其中的12组数据进行分析,结果表明,蔗糖衍生物的甜度与其本身的总能量的大小有着密切的关系,并计算分子的电荷分布,从电荷分布进一步证明它们之间的关系,经过分析得出结论:运用该模型,能够通过计算蔗糖衍生物总能量的大小预测其他卤代蔗糖的甜度的大小。 相似文献
35.
高速破片穿透船用钢靶剩余特性研究 总被引:7,自引:0,他引:7
着重讨论了高速(800m/s~1800m/s)柱形(或立方体形)钢破片(质量3.3g~60g)对不同厚度的某型船体钢靶(4mm~10mm)的穿透特性和剩余速度问题;首先给出穿透过程的分析模型,认为钢破片对船体钢靶的穿透能主要包括:弹、靶挤压塑性变形能和环向剪切塑性变形能;以能量分析和德.马尔模型为基础,给出了相应的半经验公式;在32组有效穿透实验测试数据的基础上,对相关系数进行数值拟合及动态修正;通过计算结果和试验测试结果的对比,得到的半经验公式能较好描述高速破片穿透船体钢板后的剩余速度。 相似文献
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以瑞典航空研究院(FFA)、东京大学及荷兰能源研究中心(ECN)的风洞实验为参照,以探究半经验公式类型的风力机尾流模型为目的,验证了Jensen模型和改进Jens-en模型。采用上述两个半经验模型,编写计算程序,然后按照上述每个风洞实验的参数,设定计算条件,计算风力机下游的无量纲风速,再分别与相应的实验值进行比较。结果表明,在各自的适用条件下,上述两个模型都能比较精确地模拟风力机尾流特性。这证明上述两模型可以用于进一步研究风力机尾流效应,以进行风电场微观选址与布局优化。 相似文献
40.
A prototype model of the mean radius flow path of a four-stage, high speed 1 MWe axial steam turbine was optimized by using
evolution algorithms, DE (differential evolution) algorithm in this case. Also the cost-benefits of the optimization were
inspected. The optimization was successfully performed but the accuracy of the optimization was slightly less than hoped when
compared to the control modeling executed with the CFD (computational fluid dynamics). The mentioned inaccuracy could have
been hardly avoided because of problems with an initial presumption involving semi-empiric calculations and of the uncertainty
concerning the absolute areas of qualification of the functions. This kind of algebraic modeling was essential for the success
of the optimization because e.g. CFD-calculation could not have been done on each step of the optimization. During the optimization
some problems occurred with the adequacy of the computer capacity and with finding a suitable solution that would keep the
algorithms within mathematically allowable boundaries but would not restrict the progress of the optimization too much. The
rest of the problems were due to the novelty of the application and problems with preciseness when handling the areas of qualification
of the functions. Although the accuracy of the optimization results was not exactly in accordance with the objective, they
did have a favorable effect on the designing of the turbine. The optimization executed with the help of the DE-algorithm got
at least about 3.5 % more power out of the turbine which means about 150 000 € cost-benefit per turbine in the form of additional
electricity capacity. 相似文献