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91.
Ahmed A. K. Mohammed Peter A. Limacher Benoît Champagne 《Journal of computational chemistry》2013,34(17):1497-1507
The finite field method, widely used for the calculation of static dipole polarizabilities or the first and second hyperpolarizabilities of molecules and polymers, is thoroughly explored. The application of different field strengths and the impact on the precision of the calculations were investigated. Borders could be defined and characterized, establishing a range of feasible field strengths that guarantee reliable numerical results. The quality of different types of meshes to screen the feasible region is assessed. Extrapolation schemes are presented that reduce the truncation error and allow to increase the precision of finite field calculations by one to three orders of magnitude. © 2013 Wiley Periodicals, Inc. 相似文献
92.
Masao Masamura 《Structural chemistry》2000,11(1):41-45
The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO– (H2O)
n
for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH3NH+
3 (CH3)2NH+
2 (CH3)3NH+ (CH3)4N+. 相似文献
93.
94.
呋喃-乙酸分子间相互作用的量子化学研究 总被引:6,自引:0,他引:6
用密度泛函理论B3LYP方法选取6-311++G(d,p)基组对呋喃-乙酸复合物进行了量子化学计算研究, 通过在相同水平下的频率振动分析发现了该势能面上6个极小值点, 其最稳定构型对应一强O…H—O型氢键, 其结合能在消除基组重叠误差后为-20.87 kJ•mol-1. 通过自然键轨道(NBO)分析, 研究了电荷转移及轨道相互作用. 通过自洽反应场(SCRF)理论中的Onsager 溶剂模型在介电常数分别为1.0, 2.247, 4.9, 7.58, 10.36, 20.7, 32.63, 38.2, 46.7, 78.39的不同溶剂环境下重新优化呋喃与乙酸势能面上最稳定构型A, 研究了溶剂对呋喃-乙酸复合物几何构型、电荷分布、偶极矩以及结合能的影响. 发现溶剂化作用增大了呋喃与乙酸分子间的结合能, 导致O…H距离减小, H—O振动频率红移. 当溶液介电常数在1.0~32.63范围时, 溶剂效应十分显著, 当介电常数大于32.63后, 溶剂化作用几乎达到了极限. 相似文献
95.
HONG Gong-Yi LI Le-MinCollege of Chemistry Molecular Engineering State Key Laboratory of Rare Earth Materials Chemistry Applications Peking University Beijing China 《中国化学》1996,14(4):289-296
Several numerical integration schemes for the evaluation of matrix elements in density functional theory calculations have been studied and compared by computational practice. The best scheme was found to be the combination of the atomic partition function proposed by Becke with the scaled generalized Gauss-Laguerre quadrature formula for radial integration suggested by Yang, which achieve the highest convergence rate to the numerical integration. With the same number of integration points, the accuracy of the calculated results by this scheme is higher by 1 to 2 orders of magnitudes than that by other schemes. The reason for achieving higher accuracy by this scheme has been proposed preliminarily. 相似文献
96.
In this work, we address two critical aspects of calculation of the free energy differences in molecular systems from molecular simulations. The first aspect involves checking whether the calculated free energy difference depends significantly on the extent of perturbation used for accomplishment of a given transformation. The second aspect of interest is to verify if the sampling errors in calculating the free energy differences between the wild-type molecule and a mutated one in its free state and in a complex are similar, or not, for a finite-length dynamic simulation. The reliability of the free energy estimates obtained from molecular simulations using thermodynamic cycles depends in part on this fact. For investigating these aspects, we use a self-transformation scheme in which a transformation of a part of a molecular system into itself is considered. We perform MD simulations of DNA fragments in which a part of a specific base is subjected to such a self-transformation. Results indicate that the estimated free energy differences do not depend significantly on the extent of perturbation used to achieve the transformation. Interestingly, the variation in the cumulative free energy difference, ΔA, with the coupling parameter, λ, depends significantly on the extent of perturbation. We examine the physical basis of the observed nature of the variation of the accumulated free energy difference, ΔA, against the λ value in the case of a self-transformation. In a thermodynamic cycle, the sampling errors due to the finite-length simulation for the molecular system are found to be similar to each other for the two perturbations (free and in a complex) justifying the use of such approach in calculating ΔΔA in molecular complexes. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 877–885, 1999 相似文献
97.
Two simple methods to calculate the area and volume called improved square gridmethod and cube cutting method are proposed in this paper. For any plane curve orspace surface satisfying certain conditions, by our method, the error of measurement isof the second infinitive order of measuring unit (the side length of the square grid or theside length of the little cube) when the unit is small enough. And when some properties ofthe curve or the surface can be found or its varying bounds can be evaluated, it is pointedout, in order to make the error smaller than any given value, how small the length of themeasuring unit should be. 相似文献
98.
本文建立了通用的滴定终点误差公式,考虑了副反应的影响,也适用于非水滴定。可用于判断准确滴定的可能性或分步滴定的可行性,选择指示剂的用量和确定最佳分析条件等。 相似文献
99.
Tuğba Akman 《Applicable analysis》2017,96(3):461-482
In this study, proper orthogonal decomposition (POD) method is applied to diffusion–convection–reaction equation, which is discretized using space–time discontinuous Galerkin (dG) method. We provide estimates for POD truncation error in dG-energy norm, dG-elliptic projection, and space–time projection. Using these new estimates, we analyze the error between the dG and the POD solution, and the error between the exact and the POD solution. Numerical results, which are consistent with theoretical convergence rates, are presented. 相似文献
100.
A posteriori error estimation for the Stokes–Darcy coupled problem on anisotropic discretization 下载免费PDF全文
Koffi Wilfrid Houedanou Bernardin Ahounou 《Mathematical Methods in the Applied Sciences》2017,40(10):3741-3774
This paper presents an a posteriori error analysis for the stationary Stokes–Darcy coupled problem approximated by finite element methods on anisotropic meshes in or 3. Korn's inequality for piecewise linear vector fields on anisotropic meshes is established and is applied to non‐conforming finite element method. Then the existence and uniqueness of the approximation solution are deduced for non‐conforming case. With the obtained finite element solutions, the error estimators are constructed and based on the residual of model equations plus the stabilization terms. The lower error bound is proved by means of bubble functions and the corresponding anisotropic inverse inequalities. In order to prove the upper error bound, it is vital that an anisotropic mesh corresponds to the anisotropic function under consideration. To measure this correspondence, a so‐called matching function is defined, and its discussion shows it to be useful tool. With its help, the upper error bound is shown by means of the corresponding anisotropic interpolation estimates and a special Helmholtz decomposition in both media. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献