A time-dependent method for computing thermal rate constants

Presented is an efficient numerical method for computing thermal rate constants for quantum systems with few, localized degrees of freedom. The starting point is the work of Miller, Schwartz and Tromp in which the rate constant is expressed in terms of an equilibrium flux-flux correlation function. The correlation function can be calculated very efficiently by using a combination of discrete momentum and coordinate representation. This saves time by replacing the matrix multiplications normally involved in evaluating propagators with fast Fourier transforms.     

A metropolis Monte Carlo method for computing microcanonical statistical rate constants

A new method of computing microcanonical statistical rate constants is presented. The method utilizes the Metropolis Monte Carlo algorithm in a manner which circumvents some of the numerical inefficiency associated with other Metropolis and “shot-gun” Monte Carlo based schemes. It is therefore expected to be useful in studies of many degree of freedom systems where numerical efficiency is crucial. Optimization of the method efficiency with respect to its adjustable parameters is examined in detail, both theoretically and in a numerical study of the T-shaped Ar₃ “inversion” process. The energy dependence of the T-shaped Ar₃ inversion rate is studied in a sample application of the method. An application to full three dimensional Ar₃ will be presented in a future study.     

A numerical method of computing the kinetic parameters

A numerical method of computing the kinetic parameters (the activation energy (E), the preexponential constant (A) and the reaction order (n)) of exothermic decomposition of energetic materials via the exothermic rate equation is presented. The values ofE, A, andn are reported for the exothermic decomposition of six typical energetic materials, 1,6-diazido-2,5-dinitrazahexane (I), 1,5-diazido-3-nitrazapentane (II), 2,2,4,7,9,9-hexanitro-5-methyl-4,7-dinitrazadecane (III), 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate (IV), 1,4-dinitro-2,3-dioxo-1,4-dinitrazacyclohexane (V) and 1,3,5-trianitro-1,3,5-triazafurazano[3,4-f]cycloheptane (VI).

     

A discretization method for computing chain length distributions

The method of Kumar and Ramkrishna is a numerical technique to solve population balance equations (PBEs) by discretization while preserving two moments of the distribution. When the method is used to calculate chain length distributions in polymerization reactions, the polydispersity, which depends on the first three moments of the distribution, cannot be estimated correctly. This work presents a modification of the method that allows to preserve three moments and thus calculate the polydispersity correctly, independently of the number of grid points. The modified method is applied to a model of controlled radical polymerization via RAFT and compared with the original one.     

Simplified version for the numerical determination of potential constants

Dnepropetrovsk Chemical Engineering Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, pp. 166–167, January–February, 1992.     

Eyringpy: A program for computing rate constants in the gas phase and in solution

Eyringpy is a modular program for calculating thermochemical properties and rate constants for reactions in the gas phase and in solution. The code is written in Python and it has a user-friendly interface and a simple input format. Unimolecular and bimolecular reactions with one and two products are supported. Thermochemical properties are estimated through canonical ensemble and rate constants are computed according to the transition state theory. One-dimensional Wigner and Eckart tunneling corrections are also available. Rate constants of bimolecular reactions involving the formation of pre-reactive complexes are also estimated. To compute rate constants in solution, Eyringpy uses the Collins–Kimball theory to include the diffusion-limit, the Marcus theory for electron transfer processes, and the molar fractions to account for the solvent pH effect.     

A method of computing multicenter integrals

A transformation analogous to the transform to the center-of-mass system is used to derive simple formulas for these integrals. A method of computation is used which involves expansion of the radial wave functions with respect to functions of an isotropic harmonic oscillator. It is shown that all the multicenter integrals in the case of an isotropic-oscillator function are expressed as finite sums, and that it is sufficient to use the known values for the unitary unimolecular groups SU₃ and SU₂ in order to compute these integrals.     

A novel method for calculating rate constants of diffusion-influenced reactions

In the present work we suggest a method for calculating rate constants of chemical processes affected by mobility of reactants. The method is based on the encounter theory. Unlike the widely accepted model of collision complexes it provides a general formal solution for practically arbitrary reaction scheme.     

一种预测药物活性的神经元计算新方法

提出一种基于全变异算子遗传算法(MGA)的神经元计算新方法,用于辨识复杂药物构效关系。在MGA中,表达变量的各基因使用不同的变异概率,以便提高局部搜索效率。通过将随机初始化技术与局部搜索策略相结合,该算法能在有限时间内得到满意解。使用74个抑制还原酶的嘧啶类化合物所组成的数据集作为构效关系神经元计算的典型对象,用来考核MGA法在预测药效活性计算中的有效性。交叉验证及活性预测试验表明,用MGA法建立的构效关系模型的预测能力优于其他方法。     

A kinetic method for determining intermediate instability constants of cuprous complexes

Summary The oxidation with molecular oxygen of the cuprous complex, [Cu(phen)₂]ClO₄, (phen = 1,10-phenanthroline) in dimethylsulfoxide solution was studied, and the associated intermediate instability constants were calculated from kinetic data. The results have been compared with values obtained by spectrophotometric methods.     

Recurrent equations of physicochemical constants for homologs substantiated with numerical sequences

The applicability of the unified first order recurrent equations A(n + 1) = aA(n) + b to the approximation of the physicochemical constants of various organic compounds (not only members of homologous series), previously found for normal boiling points, was extended to the dielectric constant (ε). This tendency is equivalent to the general procedure for calculating the ε of any compound from the data for preceding homologs with an accuracy comparable to the average interlaboratory reproducibility of the results of ε measurements. To substantiate this universal character of recurrent relations we consider the analogy between the constants of successive homologs and the recursive numerical sequences (Fibonacci and Padovan sequences versus Lucas and Perrin sequences, respectively).     

A computational method for approximate evaluation of ionization constants from potentiometric data

A general equation is given for the evaluation of proton dissociation constants from potentiometric data. The method is applicable to monobasic acids, and also polybasic acids, where the successive dissociation steps may or may not overlap. A computer program was employed for the calculations. The method was tested by evaluation of the constants for 22 acids, from monobasic to octobasic, with satisfactory agreement with literature data.     

A versatile method for molecular structure determinations from ground state rotational constants

A new procedure is described to determine the geometrical structure of a molecule. It starts from measured ground state rotational constants of isotopically substituted species. Internal structural parameters such as bond lengths, bond angles and dihedral angles are directly fitted with a suitable least-squares algorithm. The new method for structure determination is compared to the usual Costain—Kraitchman substitution method. It contains less stringent conditions than the latter, permits a broad range of applications and provides a reliable molecular structure.     

底物固相分散法测定土壤中甲氰菊酯残留量

以甲氰菊酯为分析对象，将一种新型的样品预处理技术-底物固相分散法(MSPD)应用于测定土壤中农药残留。确定了MSPD法的实验条件：土壤量为4g，水的加入量为1mL，固相吸附剂弗罗里硅土的用量为10．0g，淋洗剂为15mL石油醚-乙酸乙酯(1 9)。土壤样品在此条件下处理后无需进一步净化即可用气相色谱／电子捕获检定器测定。三种土壤的三种加标水平的回收率均在90％以上，相对标准偏差小于5％(n＝5)，最小检出质量比为0．002mg/kg。     

A general simulation method for computing conformational properties of single polymer chains

Rotational isomeric state (RIS) theory is the standard method for computing the conformational statistics of polymer chains. It applies to chains under theta conditions, either in the melt or in theta solution. RIS statistical weights can also be used in a Monte Carlo scheme for generating independent chain conformations with the correct statistics. One practical drawback of RIS methods is that statistical weights must be derived before any chain properties can be calculated. This can be tedious for all but relatively simple chains. Here, an efficient method is presented for computing the properties of theta chains without the intermediate step of deriving statistical weights. The method—‘RIS’ Metropolis Monte Carlo (RMMC) simulation-allows computation of the same type of properties as does RIS theory. It shares certain approximations with RIS theory but is not, strictly speaking, a rotational isomeric state method, as it allows bond torsion angles to vary continuously.     

A new method for computing surface tension using a drop of liquid

In the simulation of a liquid drop it is expensive to calculate the excess pressure and obtain the surface tension by the Laplace formula. We use the Kelvin formula which only requires the vapour density, or at most the virial pressure. Some results are given for a Lennard-Jones 12-6 fluid.     

Modified perturbation-variation method for calculating spin-spin coupling constants

Fermi contact nuclear spin-spin coupling constants are calculated by a perturbation-variation method. The trial function used includes a singularity at the nucleus and a variational term. Application to the HD molecule was carried out with an LCAO MO wavefunction expanded over a minimal Slater basis set. Using reasonable values of atomic orbital exponents α the calculated values bracket the experimental value of J_HD.     

A new method for the determination of thermodynamic equilibrium constants in separation processes

A new approach to the determination of thermodynamic equilibrium constants in ion-exchange and solvent extraction processes is described. A plot of the logarithm of the distributing species activity in the aqueous phase as a function of its concentration in the non-aqueous phase has an inflection point. The ordinate of the inflection point gives directly the logarithm of the thermodynamic equilibrium constant of the reaction considered. This was made possible by finding that the ratio between n power of the free extractant molecule (or free site) activity and the activity of the distributing species-extractant complex is unity as this point.