XYG3型双杂化密度泛函方法新进展：从能量到能量的解析梯度

本文回顾了现代密度泛函理论的基础,着重评述了XYG3型双杂化(XYG3 type of doubly hybrid,xDH)泛函的最新进展,解析能量梯度的实现.XYG3是首个依照绝热途径理论建立的双杂化泛函,在具体实现上具有独特的构架.该类型泛函利用常用泛函(如B3LYP或PBE0等)作母泛函来进行自洽计算,以期获得更好的密度和轨道,然后将所得到的轨道和密度信息带入到xDH泛函中以得到最终能量.由于自洽泛函和最终能量泛函不同,因而在计算解析能量梯度时需要求解耦合微扰Kohn-Sham方程.在此基础上,还评述了xDH泛函在能量,尤其是构型优化方面的具体表现.测试的构型集包括以共价键键合的分子和非键相互作用体系的平衡结构,以及反应过渡态结构.结果表明,xDH双杂化泛函总体上给出了比母泛函更好的能量和几何构型.

新一代密度泛函方法XYG3

大量的应用研究测试表明,以B3LYP为代表的传统密度泛函方法在反应能垒以及非键相互作用等重要性质的预测上存在困难,并且预测精度随研究体系的增大而不断变差。开发越来越精确的交换相关泛函是现代密度泛函理论发展的主线。近年来,引入未占轨道信息的新一代双杂化密度泛函方法的研究受到越来越多的关注。本篇综述回顾了这一领域已取得的一些进展;推导了双杂化泛函方法在Kohn-Sham密度泛函理论框架下的理论基础;依据各自特点,将现已提出的双杂化泛函划分为三种类别。本文着重测评了以XYG3为代表的一类双杂化泛函的表现。最后,就双杂化泛函的未来发展方向,提出了一些设想与建议。

Pyrolysis of D-Glucose to Acrolein

Despite of its great importance, the detailed molecular mechanism for carbohydrate pyrolysis remains poorly understood. We perform a density functional study with a newly developed XYG3 functional on the processes for D-glucose pyrolysis to acrolein. The most feasible reaction pathway starts from an isomerization from D-glucose to D-fructose, which then undergoes a cyclic Grob fragmentation, followed by a concerted electrocyclic dehydration to yield acrolein. This mechanism can account for the known experimental results.

Assessment of Some Density Functional Theory Methods and Force Field Models in Describing Various Interaction Modes of Benzene Dimer

Benzene dimer （bz2） is the simplest prototype of the π-π interactions. Such interactions are ubiquitous in diverse areas of science and molecular engineering. In the present work, we have made assessment on some modern density functional methods including B97-D, BLYP-D3, M06-2X, XYG3, and force field models including CHARMM, AMBER, MM3, AMOEBA on six important interaction modes of bz2. Our results not only highlight the usefulness of these cost-effective methods, which can be used as economic substitutes of the expensive CCSD（T） for complex real-world systems, but also indicate their weakness in the description of the π-π interactions, which points to the future direction for further improvements.

Theoretical Analysis of an Anion-πComplex:I-·C6F6

Recently,AnstÖter and co-workers[J.Am.Chem.Soc.141,6132(2019)]have provided the first photoelectron spectroscopic determination of the anion-πbond strength(De)using iodide-hexafluorobenzene(I-·C6F6)as the archetypical system.In combination with an equation-of-motion coupled cluster theory,namely EOM-IP-CCSD(d T),using Dunning’s aug-cc-p VDZ(a VDZ)basis set,Dein I-·C6F6 was found to be-0.53 e V with an uncertainty less than±0.03 e V.The interaction was claimed to arise for a large part from correlation forces(41%)with only a 23%contribution from electrostatic forces.In the present work,we performed the coupled-cluster with single and double and perturbative triple excitations,CCSD(T),calculations.We found that CCSD(T)/a VDZ can have an uncertainty up to 0.113 e V due to the basis set incompleteness.Our calculations disclosed that the previous calculations on the electrostatic contribution are concealed by the contributions from the exchange and Pauli repulsion.The electrostatic contribution is actually determinant,being more than double of the correlation contribution in the I-·C6F6 complex at the equilibrium binding distance.

Calculations of ionization energies and electron affinities for atoms and molecules: A comparative study with different methods

In the present work,we examined the performance of 36 density functionals,including the newly developed doubly hybrid density functional XYG3(Y.Zhang,X.Xu,and W.A.Goddard Ⅲ,Proc.Natl.Acad.Sci,USA,2009,106,4963),to calculate ionization energies(IEs)and electron affinities(EAs).We used the well-established G2-1 set as reference,which contains 14 atoms and 24 molecules for IE,along with 7 atoms and 18 molecules for EA.XYG3 leads to mean absolute deviations(MADs)of 0.057 and 0.080 eV for IEs and EAs,respectively,using the basis set of 6-311+G(3df,2p).In comparison with some other functionals,MADs for IEs are 0.109(B2PLYP),0.119(M06-2X),0.159(X3LYP),0.161(PBE),0.162(B3LYP),0.165(PBE0),0.173(TPSS),0.200(BLYP),and 0.215 eV(LC-BLYP).MADs for EAs are 0.090(X3LYP),0.090(B2PLYP),0.102(PBE),0.103(M06-2X),0.104(TPSS),0.105(BLYP),0.106(B3LYP),0.126(LC-BLYP),and 0.128 eV(PBE0).