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991.
Maíra A. Carvalho Joo Bosco P. Da Silva Marcelo Z. Hernandes 《International journal of quantum chemistry》2005,102(4):379-386
The molecular electrostatic potential (MEP) of the indole molecule was calculated in a three‐dimensional grid in which the molecule was centered at the origin. To evaluate the dependence of MEP on the type of calculation, semiempirical, ab initio, and density functional theory methods with different basis sets were employed. The data matrix generated by these calculations was analyzed by principal component analysis (PCA). The appearance of outliers and the effect of wavefunction modifications such as the introduction of electron correlations and diffuse functions were highlighted by the use of PCA. The spatial localization of such effects around the molecule was possible from the loadings values associated with the graphical analysis of the grid points. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
992.
Nikos G. Tsierkezos 《Journal of solution chemistry》2007,36(10):1301-1310
The reduction of benzophenone (Bzph) in 3-pentanone (PEN), acetone (ACE), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (ACN) and dimethyl sulfoxide (DMSO) with n-tetrabutylammonium hexafluorophosphate (TBAPF6) as background electrolyte was studied using the technique of cyclic voltammetry at the temperature of 263.15 K. The half-wave potentials (E 1/2) were extracted. The reduction of Bzph occurs in two successive one-electron steps to produce first the free radical anion Bzph− and then the dianion Bzph2−. The results indicated that the radical anion Bzph− is reoxidized to Bzph in all investigated solvent media whereas the dianion Bzph2− is reoxidized to Bzph− only in THF. The heterogeneous electron-transfer rate constants (k s ) were evaluated by employing the electrochemical rate equation proposed by Nicholson. The rate of electron transfer for the Bzph/Bzph− couple was found to be relatively slow in all investigated solvent media. Consequently, the electron-transfer processes can be recognized as quasi-reversible. The diffusion coefficients (D) of Bzph in the investigated solvent media have been calculated using the modified Randles-Sevcik equation. The effect of the physical and chemical properties of the solvent medium on the electrochemical behavior of Bzph has been examined. 相似文献
993.
Jian Wang Xing‐You Xu Lu‐De Lu Xu‐Jie Yang Wei‐Xing Ma Xiang‐Ning Cui 《Surface and interface analysis : SIA》2007,39(6):482-486
The streaming potential of supersaturated solution of binary carboxylic acids, which have even carbon atoms, was determined to characterize crystallization under different temperatures. The value of the streaming potential was related to the type and solubility of the acids and the starting temperature of crystallization, and was easily influenced by the pressure difference of the liquid or the rate of temperature decline. When the temperature was declined to the point where a crystal nucleus appeared, the streaming potential reached the minimum. Thereafter, as the temperature was sequentially lowered, some minicrystals grew, and the streaming potential presented an ascendant tendency. The higher the starting temperature of the acids saturated solution, the higher is the temperature corresponding to the streaming potential minimum. The less the carbon atoms in the acids and the greater the solubility of the acids are, the higher is the temperature of the streaming potential minimum. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
994.
We propose a general model for describing the phenomena of phase coexistence in relation to pressure induced phase transformations by means of the T–P distribution in statistical thermodynamics. Using the well‐known B1–B2 transition in NaCl as a prototype, we demonstrate how phase coexistence gives rise to the changes in the bulk modulus and the equation‐of‐state across the transition. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
995.
The photochemical reaction channels of cyclobutanone have been studied at the CASSCF level with a 6‐31G* basis set. Starting from the n‐π* excited‐state (S1) cyclobutanone, the three reactions can take place: decarbonylation (produce CO and cyclopropane or propylene), cycloelimination (produce ketene and ethylene), and ring expansion (produce oxacarbene). Our computation indicates that decarbonylation products CO and triplet trimethylene are formed on the triplet n‐π* excited state (T1) in a stepwise way via a biradical intermediate after intersystem crossing (ISC) to T1 from S1. And, then, the triplet trimethylene undergoes a second ISC to the ground state (S0) to produce the singlet trimethylene from which cyclopropane can be produced rapidly only overcoming a 1 to 2‐kcal/mol barrier while propylene can be formed as a secondary product. The cycloelimination products ketene and ethylene are formed on the S0 in a concerted mechanism after internal conversion (IC) to S0 from S1 via a biradical conical intersection. The reaction channels corresponding to ring expansion on the S0, T1, and S1 states have also been discussed, and the likeliest reaction path is that oxacarbene is formed on the ground state following S1/S0 internal conversion. The surface topology of cyclobutanone on the S1 surface is characterized by a transition state separating the minimum from the S1/S0 conical intersection, which is consistent with the previous computations and can explain the wavelength dependence of the fluorescence emission yield. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
996.
结合改进后的多松弛伪势模型, 使用格子Boltzmann方法对附壁空化泡溃灭演化过程进行了数值模拟及分析, 着重研究了壁面润湿性对附壁空化泡溃灭的影响规律. 首先, 对改进后的多松弛伪势模型开展了热力学一致性验证, 通过对比气液共存密度的数值解与解析解, 选取了满足热力学一致性需求的参数, 使得模型能够实现大密度比多相流动的数值计算; 然后, 对不同壁面润湿性条件下的附壁空化泡平衡接触角进行了数值模拟, 分析了壁面润湿性与附壁空化泡平衡接触角的关系, 分析表明: 随着壁面与流体相互作用强度的增大, 平衡接触角逐渐增大, 壁面润湿能力逐渐减弱. 进一步, 对附壁空化泡的溃灭问题进行建模, 处理了相应的边界格式, 完成了附壁空化泡溃灭过程的数值计算, 并分析了不同壁面润湿能力对附壁空化泡溃灭的影响规律; 当初始空化泡内外压差及形态相同时, 增强壁面疏水性缩短了空化泡溃灭的时间. 特别是, 壁面润湿性由亲水逐渐变为疏水时, 最大溃灭压力先降低后又逐渐升高, 而最大溃灭速度随着壁面疏水性的增强而持续升高. 研究结果揭示了壁面润湿性对附壁空化泡溃灭的影响规律, 为进一步抑制附壁空化泡溃灭的破坏效应及利用空化泡溃灭效应实现工程应用提供了理论指导.
相似文献997.
采用多参考组态相互作用(MRCI)方法,结合aug-cc-pV6Z(AV6Z)基组,计算了C2+(X4Σg-,14Σu+)的势能曲线,计算过程中考虑了Davidson修正和相对论效应,并将结果外推至完备基组(CBS)的极限.基于得到的单点能量,用最小二乘法方法进行了Murrell-Sorbie函数拟合,得到了势能函数解析式(APEF).基于APEF,计算了C2+(X4Σg-,14Σu+)离子体系的离解能De,平衡核间距Re,光谱常数ωe,ωeχe,Be,αe,结果与实验和其他理论计算值符合... 相似文献
998.
在晶格间的Tersoff势作用下分别研究了单晶体系和多晶体系中的波动传播特性。首先,在微振动的情况下,分别基于晶格间线性作用、Tersoff势作用以及含缺陷的Tersoff势作用3种势能函数研究了单晶体系中格波的传播,得到了晶格中的色散关系以及格波波速的表达式。其次,分别以碳晶格和硅晶格为例,运用有限差分方法,研究了3种势能作用下单晶体系中的波动传播过程,对比了压缩和拉伸冲击下晶格的运动差异,并讨论了入射速度对位移峰值和受力峰值的影响,揭示了单晶体系中波动传播与连续介质中波动传播的差异。最后,分别以金刚石和碳化硅为例,采用分子动力学模拟方法,研究了多晶体系中的波动传播特性,讨论了不同空间位置原子的运动差异。结果表明：多晶体系中晶格结构更复杂,其中的波动传播特性与单晶体系存在差异;缺陷的存在对波动传播规律影响显著,这种影响在多晶体系中表现得更加突出。 相似文献
999.
Xiuli Xu;Xueke Pu ;Xiaoyu Xi 《Discrete and continuous dynamical systems》2025,30(10):3858-3881
This paper considers the quantum magnetohydrodynamic model for quantum plasmas with potential force. We prove the optimal decay rates for the higher order derivative of the global small solution to the stationary state in the whole space. Specially, we show the optimal $ dot{H}^{k} $ decay rate $ sim (1+t)^{frac{3}{4}+frac{k}{2}} $, which improves the work of Xu and Pu (Discrete Contin. Dyn. Syst. Ser. B, 26, 2021). The proof is based on the optimal decay of the linearized equations, multi-frequency decompositions, and nonlinear energy estimates. 相似文献
1000.
T. Q. Dang 《国际流体数值方法杂志》1993,16(9):777-791
This paper summarizes a combined analytical-computational technique which models vortex sheets in transonic potential-flow methods. In this approach, the inviscid nature of discontinuities across vortex sheets is preserved by employing the step function to remove singularities at these surfaces. The location and strength of the vortex sheets are determined by satisfying the flow-tangency boundary condition and the vorticity transport equation. The theory is formulated for the general three-dimensional case, but its application is confined to the problem of computing slipstreams behind propellers with free-vortex blading in axisymmetric flows. 相似文献