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十字交叉法的导出和运用 总被引:1,自引:0,他引:1
十字交叉法也称图解法,作为一种简化的解题方法,应用于二元混合体系具有平均值的计算问题,它具有简化思路、简便运算、计算速度快等显著优点。近年来,十字交叉法在中学化学计算中广泛使用,有许多高考题也可用此法快速求解。但是,到目前为止,一些书刊对该方法的介绍仅仅局限于简单推导、应用的范畴,且应用时始终把平均值放在“十字”的中间,而没有把通过十字交叉得到差值的比值的含义如何确定讲清楚, 相似文献
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依据终点误差的体积比定义式,滴定分析中所加入滴定剂的体积与待测体系的初始体积之比是计算终点误差的关键。建立了配位滴定中关于体积比的一般方程,提出了求解该方程的迭代策略,并给出了终点误差的计算实例。结果表明,该方法具有适应范围广、计算精度高的特点。 相似文献
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本文将前文~[1,2]建议的直接计算交替烃HOMO(最高占据分子轨道)、LUMO(最低未占分子轨道)能量的方法推广到非交替烃。在HMO近似内, 对非交替烃分子的邻接矩阵联合应用逆迭代和Rayleigh商, 只需迭代一次就能得到该分子HOMO(或LUMO)能量的足够精确的结果。文中提出了计算的格式, 说明了选择初始变分函数的原则。用这种方法, 计算了30个分子的前线轨道~[3]能量, 平均误差为0.002β。本文提出了计算LOMO(最低占据分子轨道)能量的拓扑公式, 它同时适用于交替烃和非交替烃, 其计算精度要优于文献中曾经报道过的结果。用例子说明了方法的应用。 相似文献
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离子选择性电极分析中的多次标准加入法的一种非线性算法 总被引:1,自引:0,他引:1
离子选择电极分析的多次标准加入法的实验数据处理通常采用图解法或计算机解法。用计算机求解具有速度快、精度高等优点,目前被广泛采用。1970年Brand提出一种非线性最小二乘法求解C_x、S和E。的Fortran计算程序。其解法是用Taylor级数展开将非线性方程转化为线性法方程,用消元法解法方程,经过迭代计算求得结果。石守衡等人对Bra-ad解法进行改进,提出用共轭斜量法解矛盾方程组,无须形成法方程,从而提高了运算精度 相似文献
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借鉴数学中求方程根的二分迭代法精确计算难溶电解质在水解、酸化、络合后的溶解度,在估计出[H+]的大致范围后,再选定迭代精度。当正电荷总浓度与负电荷总浓度之相对偏差小于迭代精度时,即可认为正电荷总浓度与负电荷总浓度相等,计算结束,得到结果。本方法能计算出传统方法无法计算的化合物的溶解度、pH及水解产物的浓度。 相似文献
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Gerard P. Jellison John B. Greenshields J. Clifton Hill 《Theoretical chemistry accounts》1981,60(1):1-10
HeH++ was selected as a simple model for the comparison of relative efficiencies of single and multi-centered Gaussian functions in computing molecular orbitals and their corresponding energies. One-, two-, and three-center linear combinations of twelve basis functions were applied to the calculation of potential curves for the ground state and lowest two excited sigma states of HeH++. A point-by-point comparison was made with the same states generated by an exact solution calculation. This comparison demonstrated that the multi-centered functions were capable of reproducing energy minima, potential curve crossings and dissociation modes in agreement with the exact calculation. The single center functions were not capable of duplicating this behavior. 相似文献
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The calculation of single-particle time correlation functions using the Bose-Einstein centroid dynamics formalism is discussed. A new definition of the quasidensity operator is used to calculate the centroid force on a given particle for an anharmonic system. The force includes correlation effects due to quantum statistics and is used for the calculation of the classical-like dynamics of phase-space centroid variables within the centroid molecular dynamics approximation. Time correlation functions are then obtained for single-particle quantities. These correspond to the double-Kubo transform of exact quantum-mechanical correlation functions. The centroid dynamics results are compared to those of exact basis-set calculations and a good agreement is found. The level of accuracy is in fact the same as what was observed earlier for the calculation of center-of-mass correlation functions for Fermi-Dirac and Bose-Einstein statistics, and for any correlation function for Boltzmann statistics. These results show that it is now possible to use Bose-Einstein centroid molecular dynamics to calculate single-particle correlation functions for systems where quantum exchange effects are present. 相似文献
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The application of the Σ-separation method to the calculation of multicenter two-electron molecular integrals with Slater-type basis functions is reported. The approach is based on the approximation of a scalar component of the two-center atomic density by a two-center expansion over Slater-type functions. A least-squares fit was used to determine the coefficients of the expansion. The angular multipliers of the atomic density were treated exactly. It is shown that this approach can serve as a sufficiently accurate and fast algorithm for the calculation of multicenter two-electron molecular integrals with Slater-type basis functions. © 1995 John Wiley & Sons, Inc. 相似文献
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Configuration interaction calculations of electronic wave functions for atoms and molecules have generally been limited to relatively small basis sets because of the exponential increase in the number of configurations as basis functions are added. While higher than quadruply excited configurations are of negligible importance in CI wave functions, it is shown that the effect of triple and quadruple excitation configurations can be substantially included even when the matrix elements between such configurations are neglected, leaving only their diagonal elements and the elements connecting them with the single and double excitations. This approximation is seen to be formally practically equivalent to a first-order perturbation expression for the wave function (second-order for the energy) based on an optimum linear combination of the zero, single, and double excitation configurations as the zero-order function. If suitable procedures are used, the amount of computational effort involved in such a calculation is roughly proportional to the fourth power of the number of basis functions employed, thus preventing the CI stage of the calculation from increasing in magnitude much faster than the stages involving the calculation and manipulation of the elementary integrals. 相似文献
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E. Recami 《International journal of quantum chemistry》1980,17(1):37-40
An advantage of modified virtual orbitals of Hartree–Fock method is discussed in the calculation of the second-order perturbation energy. All the modified virtual orbitals can be fitted for the intermediate virtual states in the perturbation expansion, only if the molecular orbitals are expanded in terms of infinite basis functions and the set of molecular orbitals is infinite and complete. If the molecular orbitals are expanded in terms of finite basis functions, only the modified virtual orbitals with lower energies are appropriate to describe the intermediate virtual states, but the modified virtual orbitals with higher energies become inadequate. To explain the usefulness of the modified virtual orbitals, the calculation by the modified Hartree–Fock method without CI are compared with the calculation by the traditional Hartree–Fock method with complete CI . 相似文献
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六十年代后期,在Hartree-Fock-Slater法的基础上,提出了Xα法[1].用于原子结构计算的Xα法与HF(Hartree-Fock)法的主要区别在于:用简单的统计平均交换势替代了HF法中计算最为困难的电子交换势,从而在保持较高理论严谨性和计算精确度的同时,大大减少了计算工作量,近年来获得了广泛的应用.我们尝试用经过适当修改的Xα方法,计算原子参数,解决分子结构中的某些问题.用原子参数解决分子问题,历来是化学和物理工作者常用的方法.本工作的意图是引入一个比HF法简单的容易在微机上实现的某种表现原子参数的计算方法,提供… 相似文献
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Three different forms of perturbation theories, variational perturbation, finite perturbation and second-order, are evaluated regarding their value for calculation of electronic polarizabilities of small and intermediate size molecules. It is concluded that with the practical constraint of a small basis set the variational perturbation method is the most promising alternative for calculation of polarizabilities. For several small molecules, our calculated polarizabilities indicate that both IEHT and ab initio wave functions give values in close agreement with each other. Variational perturbation calculations of polarizabilities with IEHT wave functions also include the DNA bases. 相似文献
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V. M. Tapilin 《Journal of Structural Chemistry》2002,43(2):195-200
Energy band position and formation energy of copper and platinum crystals were calculated using a conventional basis set of atomic functions and a basis of trimmed functions with polynomial tails. A comparison between the results shows that the accuracy of calculation in the basis of trimmed functions is not worse than the accuracy of calculations in the standard basis, while the computing time is 2 times smaller. 相似文献
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The calculation of the diffusion coefficients of nonionic surfactants as functions of their concentrations in micellar solutions has been analyzed within the framework of the quasi-chemical version of the law of mass action. The methods of the introduction of initial calculation parameters, calculation scheme for an ideal mixture of monomeric molecules and micelles, and corrections for varying solution viscosity have been considered. Numerical estimations have been performed using aqueous tetraoxyethylene octyl ether, pentaoxyethylene hexyl ether, and octyl-β-D-glucopyranoside solutions as examples. 相似文献
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We study the quantum dynamics in a model system consisting of two electrons and a nucleus which move between two fixed ions in one dimension. The numerically determined wave functions allow for the calculation of time-dependent electron localization functions in the case of parallel spin and of the time-dependent antiparallel spin electron localization functions for antiparallel spin. With the help of these functions, it becomes possible to illustrate how electronic localization is modified through the vibrational wave-packet motion of the nucleus. 相似文献