Study on Pair Correlation Energies of Isoelectronic Systems F^－, HF and H2F^＋

The intrapair and interpair correlation energies of F-, HF and H2F^ systems are calculated and analyzed using MP2-OPT2 method of MELD program with cc-PVSZ^* basis set. From the analysis of pair correlation energies of these isoelectronlc sysoterns, it is found that the 1sF^2 pair correlation energy is trans-ferable in these three isociectronic systems. According to the definition of pair correlation contribution of one electron pair to a system, the pair correlation contribution values of these three systems are calculated. The correlation contribution values of inner electron pairs and H—F bonding electron pair in HF molecule with those in H2F^ system are compared. The results indicate that the bonding effect of a molecule is one of the im-portant factors to influence electron correlation energy of the system. The comparison of correlation energy contributions in-cluding triple and quadruple excitations with those only includ-ing singles and doubles calculated with 6-311 G(d) basis set shows that the higher.excitation correlation energy contribution gives more than 2 % of the total correlation energy for these sys-tems.     

强离子键体系电子相关能简捷计算方案的应用

The calculation results of electron correlation energies of KF and （KF）2 were reported. The transferability of 1s^2 K , 1s^2 F and the inner core correlation effects of K and F in both K, K^＋, KF and F, F^-, KF systems were investigated respectively. The correlation energy contributions of K and F component to KF system were calculated. By applying the simple estimation scheme to the calculation of the correlation energy of the strong ionic compound KF and （KF）2, it was shown that such a powerful scheme could not only reach the chemical accuracy but also need little computational work.     

Simple estimation of electron correlation energy for multi-atomic strong ionic compounds KX and (KX)2 (X=OH, NC)

On the basis of the calculations and analyses of the intrapair and interpair correlation energy of KX (X = OH, NC) molecules and the results of the transferability of both the innermost intrapair correlation energy and the inner core effect of K and X in KX molecules, we defined and calculated the K^δ+ and X^δ-correlation contributions to the total correlation energy of KX molecules. With the comparison of the pair correlation energy of K⁺, X^- and KX systems, we present a simple estimation method to estimate the electron correlation energy of strong ionic compound by summarizing the correlation energy of its constituent ion and ionic group. By using this simple method, the reasonable estimation results of the correlation energy of (KOH)₂ and (KNC)₂ have been obtained at mp2/6-311++G(d) level with Gaussian98 program, and the deviations are very small. Applying the scheme of “Separate Large System into Smaller Ones” to the calculation of electron correlation energy of large ionic compounds, it can not only save lot of computation work but also reach the chemical accuracy.     

基团贡献法估算线性烷基醇分子体系电子相关能

在本文中,提出了极性基团电子相关能贡献的定义,并在MP2-OPT2/6-311++G(d)水平上计算了CH₃(CH₂) _mOH( m=0-4)体系中HO-、CH₃-和-CH₂-基团电子相关能贡献值。计算结果表明,在CH₃(CH₂) _mOH( m=0-4)体系中端基HO-、CH₃-基团电子相关能贡献值 E_corr(HO-)和 E_corr(cH₃-)的数值随着 m的增加而逐渐减小。同一体系中a -CH₂-基团电子相关能贡献值大于其它-CH₂-基团电子相关能贡献值,在CH₃(CH₂) _mOH( m=1-4)体系中,距离端基HO-基团越远的-CH₂-基团其电子相关能贡献值越小;通过计算结果可以推断,在CH₃(CH₂) _mOH体系中随着 m的逐渐增加,相对远离端基HO-的-CH₂-基团的电子相关能贡献值表现出收敛趋向并将趋于不变,此-CH₂-基团可看作一个标准的亚甲基而且其 E_corr(-cH₂-)的数值在CH₃(CH₂) _mOH体系中具有传递性。在MP2-OPT2/6-311++G(d)水平上对CH₃(CH₂) _mOH( m=2-4)体系的计算结果和应用Gaussian 98程序在MP2/6-311++G(d)//HF/6-311++G(d)水平上对CH₃(CH₂) _mOH( m=2-7)体系的计算结果均表明,体系总电子相关能与（ m-1）呈 中 m是体系中亚甲乙烯基的数值。     

Two Typical Examples of Scaling Ionic Partition Scheme for Estimating Correlation Energy of A2 Type Molecules

Based on the calculation results of pair correlation energy contributions of the various electron pairs in Na2 and H2NNH2 systems and the application of the scaling ionic partition scheme for symmetrical A2 type systems, the total correlation energies of Na2 and H2NNH2 have been reproduced by using this simple scheme. The two results show that the absolute deviations are within an acceptable range of error, however, in this way, more than 90% of computational work can be saved. The most attractive result in present paper is that, in these two molecules the coefficients c1 and c2 in the estimation equation can be obtained by the proportion of correlation energy of A^- to that of A^ singlet system. Therefore, it is believed that the proposed ionic partition scheme for symmetrical A2 molecules would be very useful to estimate the correlation energies of large symmetrical molecules.     

Simple estimation of electron correlation energy for multi-atomic strong ionic compounds KX and (KX)2 (X = OH, NC)

On the basis of the calculations and analyses of the intrapair and interpair correlation energy of KX (X = OH, NC) molecules and the results of the transferability of both the innermost intrapair correlation energy and the inner core effect of K and X in KX molecules, we defined and calculated the Kδ- and Xδ-correlation contributions to the total correlation energy of KX molecules. With the comparison of the pair correlation energy of K+, X- and KX systems, we present a simple estimation method to estimate the electron correlation energy of strong ionic compound by summarizing the correlation energy of its constituent ion and ionic group. By using this simple method, the reasonable estimation results of the correlation energy of (KOH)2 and (KNC)2 have been obtained at mp2/6-311++G(d) level with Gaussian98 program, and the deviations are very small. Applying the scheme of "Separate Large System into Smaller Ones" to the calculation of electron correlation energy of large ionic compounds, it can not only     

On the contribution of higher-order excitations to correlation energies: The ground state of the water molecule

Using the results of a configuration interaction calculation reported by Rosenberg and Shavitt, we derive an approximation to the correlation energy which may be associated with the sum to infinite order of all linked diagrams involving singly- and doubly-excited states. This result is compared with that obtained by calculation of the energy through third-order. The fourth-order linked diagrams involving quadruply-excited states are computed. It is shown that there is a considerable degree of cancellation between the fourth-order linked diagram energy terms involving doubly-excited intermediate states only and those which contain quadruply-excited states.     

Development of an automatic estimation system for both the partition coefficient and aqueous solubility

Summary A computer program has been developed for estimating both the partition coefficient between 1-octanol and water phases and the aqueous solubility from the structural formula. This system is an extended version of a previously described program entitled CHEMICALC for the automatic estimation of the partition coefficient. The aqueous solubility is estimated via two pathways. The first is based on the linear relationship between logarithms of the aqueous solubilities of 497 compounds and their estimated 1-octanol/water partition coefficients. In the second, combined handling of two available group contribution methods of Irmann [Chem. Ing. Tech., 37 (1965) 789] and Wakita et al. [Chem. Pharm. Bull., 34 (1986) 4663] is adopted according to compound type. Some revisions and extensions of the methods for estimating the aqueous solubility have been made in both pathways, and the accuracy of the estimated aqueous solubilities for 497 compounds is discussed.     

线性氟代烷烃电子相关能的基团加和性

应用Meld 程序在MP2-OPT2/6-311++G(d)水平计算了线性氟代烷烃分子CH3(CH2)mF(m=0-5)中—CH3、—CH2—和—F基团电子相关能贡献值. 计算结果表明, 在CH3(CH2)mF(m=0-5)体系中, 端基—F、—CH3基团电子相关能贡献值Ecorr(—F)和Ecorr(—CH3)随着m的增大而逐渐减小. 分子中α位置—CH2—基团电子相关能贡献值Ecorr(—CH2—)大于其他位置的贡献值. 通过计算结果可以推断, 在CH3(CH2)mF体系中随着m的逐渐增大, 远离端基—F的—CH2—基团电子相关能贡献值逐渐减小并将趋于不变, 此—CH2—基团可看作一个标准的亚甲基且其Ecorr(—CH2—)的数值在CH3(CH2)mF体系中具有传递性. 应用Meld程序在MP2-OPT2/6-311++G(d)水平对CH3(CH2)mF(m=2-5)体系的计算结果和应用Gaussian 98程序在MP2/6-311++G(d)//HF/6-311++G(d)水平对CH3(CH2)mF(m=2-10)体系的计算结果均表明, 体系总电子相关能与体系中(m-1)数值呈线性关系.     

Cover Feature: How Different are the Diamagnetic and Paramagnetic Contributions to Off-Nucleus Shielding in Aromatic and Antiaromatic Rings? (ChemPhysChem 9/2023)

The spatial variations in the diamagnetic and paramagnetic contributions to the off-nucleus isotropic shielding, , and to the zz component of the off-nucleus shielding tensor, , around benzene (C₆H₆) and cyclobutadiene (C₄H₄) are investigated using complete-active-space self-consistent field wavefunctions. Despite the substantial differences between and around the aromatic C₆H₆ and the antiaromatic C₄H₄, the diamagnetic and paramagnetic contributions to these quantities, and , and and , are found to behave similarly in the two molecules, shielding and deshielding, respectively, each ring and its surroundings. The different signs of the most popular aromaticity criterion, the nucleus-independent chemical shift (NICS), in C₆H₆ and C₄H₄ are shown to follow from a change in the balance between the respective diamagnetic and paramagnetic contributions. Thus, the different NICS values for antiaromatic and antiaromatic molecules cannot be attributed to differences in the ease of access to excited states only; differences in the electron density, which determines the overall bonding picture, also play an important role.     

应用基团贡献法关联抗生素的高效液相色谱的保留值

应用ＵＮＩＦＡＣ基团贡献模型计算了４种头孢菌素在ＯＤＳ柱上及不同配比甲醇－水体系中的活度系数，采用多元线性回归法关联了头孢菌素－甲醇－水体系的反相高效液相色谱的保留值，可预测不同配比流动相下的容量因子，经验证实验值与计算值的对误差小于１０％。     

Rules on intrapair and interpair correlation energy for Cl, Cl?and MCl (M=H, Li, Na, K)

According to the calculation results of the intrapair and interpair correlation energy for the title systems, it has been found that the intrapair correlation energy of K shell of Cl is almost a constant and both the intrashell and intershell correlation energy of K and L shell changes little. It has also been found that in MCl series compounds the value of Cl correlation energy contribution depends on the ionicity of MCl compounds, i.e., the Cl correlation energy contribution increases with the increase of the ionic bond strength of the compound and this value is always less than the correlation energy of Cl^- anion but always larger than that of Cl atom. These rules are helpful for the estimation of the correlation energy of ionic compounds and the energy changes of chemical reactions.     

Rules on intrapair and interpair correlation energy for Cl, Cl~(-) and MCI (M=H, Li, Na, K)

According to the calculation results of the intrapair and interpair correlation energy for the title systems, it has been found that the intrapair correlation energy of K shell of Cl is almost a constant and both the intrashell and intershell correlation energy of K and L shell changes little. It has also been found that in MCI series compounds the value of Cl correlation energy contribution depends on the ionicity of MCI compounds, i.e., the Cl correlation energy contribution increases with the increase of the ionic bond strength of the compound and this value is always less than the correlation energy of Cl" anion but always larger than that of Cl atom. These rules are helpful for the estimation of the correlation energy of ionic compounds and the energy changes of chemical reactions.     

梁树权:我国分析化学的先驱

梁树权是中国科学院院士,是我国著名分析化学家。他从事分析化学研究与教育70余年,为我国分析化学的开拓和发展做出了重大贡献。通过展示梁树权先生完整的履历,以及他杰出的科研工作,以此纪念先生逝世十周年,致以缅怀之情。     

Analysis of {[N,N-dialkylamide or 1-methyl-2-pyrrolidone] + 1-chloroalkane or α,ω-dichloroalkane} mixtures in terms of group contribution

The experimental vapour–liquid equilibria, VLE, excess molar Gibbs energies, , and excess molar enthalpies, , determined previously for the systems N,N-dimethylformamide, or N,N-dimethylacetamide, or 1-methyl-2-pyrrolidone + 1-chlorobutane, or +1-chlorohexane, or +1-chlorooctane, or +1,2-dichloroethane, or +1,4-dichlorobutane, or +1,6-dichlorohexane, are examined using the DISQUAC group contribution model. The dispersive and quasi-chemical interchange parameters for the contacts chloro-amide in the mixtures with N,N-dialkylamide or 1-methyl-2-pyrrolidone with chloro- or α,ω-dichloroalkane were calculated. The model reproduces quite well the experimental data.     

Electron correlation: the many-body problem at the heart of chemistry

The physical interactions among electrons and nuclei, responsible for the chemistry of atoms and molecules, is well described by quantum mechanics and chemistry is therefore fully described by the solutions of the Schr?dinger equation. In all but the simplest systems we must be content with approximate solutions, the principal difficulty being the treatment of the correlation between the motions of the many electrons, arising from their mutual repulsion. This article aims to provide a clear understanding of the physical concept of electron correlation and the modern methods used for its approximation. Using helium as a simple case study and beginning with an uncorrelated orbital picture of electronic motion, we first introduce Fermi correlation, arising from the symmetry requirements of the exact wave function, and then consider the Coulomb correlation arising from the mutual Coulomb repulsion between the electrons. Finally, we briefly discuss the general treatment of electron correlation in modern electronic-structure theory, focussing on the Hartree-Fock and coupled-cluster methods and addressing static and dynamical Coulomb correlation.     

Aquafac: Aqueous Functional Group Activity Coefficients

Abstract

AQUAFAC, a new group contribution method for estimating aqueous activity coefficients, has been applied to a large set of organic compounds. The current work introduces 27 new group values for hydrocarbon, halogen, and non-hydrogen bond donating oxygen groups. Group values (q-values) have been derived from a data set of 621 compounds representing over 1700 individual solubility values. No correction factors were used in generating the current group values. AQUAFAC was found to give acceptable results when applied to some environmentally important compounds.     

Prediction of Antoine constants using a group contribution method

Vapor pressure is one of the important properties necessary for process design. Antoine equation has been widely used to evaluate the vapor pressures. This article deals with the proposal of a method for predicting the Antoine constants using a group contribution method. The 1817 compounds treated here are grouped into six classes. The group contribution parameters for each class have been determined using a regression analysis. The group contribution method with help of experimental normal boiling point has good results for predicting the vapor pressures.