铝原子团簇Al5、Al5-和Al5+稳定结构的密度泛函理论研究

采用密度泛函理论的四种方法:杂化密度泛函B3LYP与B3PW91、Perdew-Wang91交换与相关泛函WP91PW91、局域自旋密度近似SVWN,研究了A15、Al5-和Al5+团簇的多种可能结构,找到了它们稳定的结构与自旋态,与已有的理论结果作了比较,并计算了Al5-的绝热与垂直电子离解能、Al5的绝热与垂直电离势,同有关的实验数据比较,符合较好.同时对四种密度泛函方法的计算结果作了一些比较与讨论.     

元素电负性和硬度的密度泛函理论研究

应用密度泛函理论的DFT LDA、DFT LDA/NL和改进的Slater过渡态方法,把元素的电离能和电子亲合能的计算扩展到周期表的103种元素.并用有限差分方法计算了这103种元素的电负性和硬度.计算中考虑了相对论效应.计算结果比以前Robles等用密度泛函理论的XGL和Xα近似的交换相关泛函的计算结果有所改进,更接近实验值.     

密度泛函理论及其数值方法新进展

综述了密度泛函理论及其数值方法的最新进展.密度泛函理论的发展以寻找合适 的交换相关近似为主线,从最初的局域密度近似、广义梯度近似到现在的非局域泛函、自相 互作用修正,多种泛函形式的相继出现使得密度泛函理论可以提供越来越精确的计算结果. 除了交换相关近似的发展,近年来密度泛函理论向含时理论、相对论等方面的扩展也很活跃 .另外,在密度泛函理论体系发展的同时,相应的数值计算方法的发展也非常迅速.从古老 的有限差分、有限元到新兴的小波分析都被用来实现密度泛函理论的数值计算.与此同时, 线性标度的密度泛函理论算法日趋成熟,使得通过密度泛函理论研究诸如生物大分子之类的 体系成为可能.随着密度泛函理论本身及其数值方法的发展,它的应用也越来越广泛,一些新的应用领域和研究方向不断涌现.     

以双亚甲胺席夫碱为配体的双核吡唑铜配合物的磁性理论研究

采用对称性破损态方法结合密度泛函理论,以双亚甲胺席夫碱为配体的双核吡唑铜配合物[Cu_2L(PZ)](L=双甲亚胺三阴离子,由1-苯基-3-甲基-4-甲酰吡唑和1,3-二氨-2-丙醇衍生而成;PZ=吡唑阴离子)作为研究对象,通过与实验数据相比较,讨论了不同密度泛函方法与基组对金属铜配合物磁交换耦合常数的影响.结果表明,4种混合密度泛函方法(B3PW91,B3LYP,B3P86和PBE)及3种单一密度泛函方法(BPW91,BLYP和BP86)的计算结果都能与实验值符号一致,且B3P86方法所得到的结果与实验值最为接近,而单一密度泛函的计算结果误差较大,与实验值吻合程度不好.同时采用B3P86方法计算所得交换耦合常数Jab对基组的依赖性较大.研究表明,2个Cu(Ⅱ)离子之间弱的反铁磁相互作用主要源于单占据分子轨道SOMOs小的能量劈裂.     

约束条件下的硬球流体

利用密度泛函理论和分子动力学方法,对处于两平行硬墙之间的硬球流体的密度分布进行了计算通过比较两种方法的结果,发现在墙之间距离较大时,Rosenfeld密度泛函理论的结果与分子动力学模拟的结果符合很好;当两堵墙间的距离很小时,这两个结果之间存在明显的不一致.另外,还研究了约束条件下密度分布的结构.     

几种密度泛函理论公式用于镧系硫属化合物计算的比较

以镧系元素La、Gd、Lu的硫属化合物为对象,系统考察几种密度泛函理论公式对镧系化合物计算的适用情况,考虑了相对论效应的影响. 计算结果显示,相对论效应引起的键长变化在十2Pm到-3Pm之间,引起的键能减小为0. 4～0. 6eV,与采用的密度泛函公式关系不明显. 不同的密度泛函公式对键长的计算结果影响也不太大,但对键能有显著影响,其中LDA(VWN)＋PW86X公式给出最好结果. 交换能梯度校正明显改善键能计算结果,而相关能梯度校正反而使之变差. 简单的X_α公式给出相当好的键能计算结果. 在考虑相对论效应和梯度校正以后,密度泛函理论方法给出比较可靠的键长数值,键能则仍然偏高,但不超过20％.     

铁磁性双核吲哚铜配合物的理论研究

采用密度泛函理论结合对称性破损态方法(DFT-BS),以双亚甲胺席夫碱为配体的双核吲哚铜配合物[Cu2L(AZ)(DMSO)](L=双甲亚胺三阴离子,由1-苯基-3-甲基-4-甲酰吡唑和1,3-二氨-2-丙醇衍生而成;AZ=7-氮杂吲哚阴离子)作为研究对象,通过与实验数据相比较,讨论了在不同密度泛函方法与基组对金属铜配物交换耦合常数的影响.结果表明,4种混合密度泛函方法(B3PW91,B3LYP,B3P86和PBE)及3种单一密度泛函(BPW91,BLYP和BP86)的计算结果都与实验值106cm-1有着相同的符号,但使用单一密度泛函所得到的结果与实验值比较接近.不论是混合密度泛函还是单一密度泛函计算所得到的耦合常数Jab对基组都有很大的依赖性,且BLYP/LANL2DZ水平下计算所得结果与实验数据吻合程度最好.研究表明,铁磁性配合物[Cu2L(AZ)(DMSO)]中存在着自旋离域和自旋极化效应.     

邻苯二甲酸单甲酯桥联双核铜(Ⅱ)配合物磁性的理论研究

采用对称性破损态方法结合密度泛函理论,选用典型的强反铁磁双核配合物作为研究对象,通过与实验数据相比较,探讨了不同密度泛函方法与基组对计算铜配合物[Cu2(mMP)4(H2O)2]·H2O交换耦合常数的准确度.结果表明,4种混合密度泛函DFT(B3LYP,B3P86,B3PW91和PBE0)的计算结果都能和实验所观察到的值-324cm-1符号一致,但B3PW91方法得到的结果和实验结果吻合程度最好,同时采用方法B3PW91方法计算所得的交换耦合常数Jab对基组的依赖性较大.研究表明,2个Cu(Ⅱ)离子之间的反铁磁相互作用主要源于单占据分子轨道SOMOs大的能量劈裂和桥联配体O-C-O轨道的重叠.     

萤光素类似物激发态的TD-DFT计算精度评估

采用含时密度泛函理论(TD-DFT)对8种已知萤光素类似物的垂直激发能和发射能进行了系统的考察.选取10种交换-相关(XC)泛函对8种萤光素类似物的基态和第一单重激发态结构、吸收和发射光谱进行了计算,并将得到的结果与实验数据进行对照.结果表明,该系列物质吸收光谱和发射光谱的计算对XC泛函的选择非常敏感.B3LYP、mPW3PBE、B3PW91方法能够提供较好理论计算结果,吸收光谱的均方根误差(RMS)在0.40eV以内,标准差(SD)在0.27eV以内;发射光谱的RMS在0.24eV以内,SD在0.17eV以内.     

3-甲基-4-对甲基苯基-5-(2-吡啶)-1,2,4-三唑桥联的双核铜配合物的磁性理论研究

采用对称性破损态方法结合密度泛函理论,选用反铁磁双核配合物[Cu2(MMBPT)2Cl4(H2O)2.5](MMBPT=3-甲基-4-对甲基苯基-5-(2-吡啶)-1,2,4-三唑)作为研究对象,通过与实验数据相比较,探讨了不同密度泛函方法与基组对计算铜配合物交换耦合常数的准确度.结果表明,4种混合密度泛函DFT(B3LYP,B3P86,B3PW91和PBE0)的计算结果都能和实验所观察到的值-31cm-1符号一致,但只有B3PW91方法得到的结果和实验结果吻合程度最好,同时采用方法B3PW91方法计算所得的交换耦合常数Jab对基组的依赖性较大.研究表明,2个Cu(Ⅱ)离子之间弱的反铁磁相互作用主要源于单占据分子轨道SOMOs小的能量劈裂.     

甲烷晶体的晶格能和弹性性质: 不同方法及泛函的评估

通过对甲烷晶体进行结构、晶格能和弹性特性的研究, 评估了不包含和包含色散能量修正的密度泛函理论的性能. 我们分别利用不包含色散能量修正的密度泛函理论(DFT) (包含不同的标准泛函和杂化泛函)和包含色散能量修正的密度泛函理论(DFT-D)计算了甲烷晶体特性, 并与实验作对比. 尽管DFT-D 与传统密度泛函理论及杂化密度泛函理论相比, 修正了甲烷晶体中的范德华(vdW)相互作用, 但是一些修正方案过分修正了这种相互作用. 因此, 人们在使用DFT-D方法时务必谨慎.     

A localized orbital analysis of the thermochemical errors in hybrid density functional theory: achieving chemical accuracy via a simple empirical correction scheme

This paper describes an empirical localized orbital correction model which improves the accuracy of density functional theory (DFT) methods for the prediction of thermochemical properties for molecules of first and second row elements. The B3LYP localized orbital correction version of the model improves B3LYP DFT atomization energy calculations on the G3 data set of 222 molecules from a mean absolute deviation (MAD) from experiment of 4.8 to 0.8 kcal/mol. The almost complete elimination of large outliers and the substantial reduction in MAD yield overall results comparable to the G3 wave-function-based method; furthermore, the new model has zero additional computational cost beyond standard DFT calculations. The following four classes of correction parameters are applied to a molecule based on standard valence bond assignments: corrections to atoms, corrections to individual bonds, corrections for neighboring bonds of a given bond, and radical environmental corrections. Although the model is heuristic and is based on a 22 parameter multiple linear regression to experimental errors, each of the parameters is justified on physical grounds, and each provides insight into the fundamental limitations of DFT, most importantly the failure of current DFT methods to accurately account for nondynamical electron correlation.     

Assessment of Contemporary Theoretical Methods for Bond Dissociation Enthalpies

The density functional theory (DFT) is the most popular method for evaluating bond dis-sociation enthalpies (BDEs) of most molecules. Thus, we are committed to looking for alternative methods that can balance the computational cost and higher precision to the best for large systems. The performance of DFT, double-hybrid DFT, and high-level com-posite methods are examined. The tested sets contain monocyclic and polycyclic aromatic molecules, branched hydrocarbons, small inorganic molecules, etc. The results show that the mPW2PLYP and G4MP2 methods achieve reasonable agreement with the benchmark values for most tested molecules, and the mean absolute deviations are 2.43 and 1.96 kcal/mol after excluding the BDEs of branched hydrocarbons. We recommend the G4MP2 is the most appropriate method for small systems (atoms number ≤20); the double-hybrid DFT methods are advised for large aromatic molecules in medium size (20 ≤atoms number ≤50), and the double-hybrid DFT methods with empirical dispersion correction are recommended for long-chain and branched hydrocarbons in the same size scope; the DFT methods are advised to apply for large systems (atoms number ≥50), and the M06-2X and B3P86 methods are also favorable. Moreover, the di erences of optimized geometry of different methods are discussed and the effects of basis sets for various methods are investigated.     

DFT Methods to Study the Reaction Mechanism of Iridium‐Catalyzed Hydrogenation of Olefins: Which Functional Should be Chosen?

To enable the selection of more accurate computational methods for the future theoretical exploration of the reaction mechanism of Ir‐catalyzed olefin hydrogenation, we compared high‐level ab initio coupled cluster and DFT calculations with a simplified model of Pfaltz's Ir/P,N‐type catalyst for all four previously proposed Ir^I/Ir^III and Ir^III/Ir^V mechanisms. Through the systematic assessment of the DFT performances, the DFT empirical dispersion correction (DFT‐D3) is found to be indispensable for improving the accuracy of relative energies between the Ir^I/Ir^III and Ir^III/Ir^V mechanisms. After including the DFT‐D3 correction, the three best performing density functionals (DFs) are B2‐PLYP, BP86, and TPSSh. In these recommended DFs, the computationally more expensive double‐hybrid functional B2‐PLYP‐D3 has a balanced and outstanding performance for calculations of the reaction barriers, reaction energies, and energy gaps between different mechanisms, whereas the less costly BP86‐D3 and TPSSh‐D3 methods have outstanding, but relatively less uniform performances.     

羰基镍簇Ni(CO)n(n=1-4)的结构和Ni-CO键解离性质的密度泛函理论研究

在密度泛函理论框架下, 应用不同泛函计算了配合物Ni(CO)n(n=1~4)的平衡几何构型和振动频率. 考察了泛函和基组重叠误差对预测Ni—CO键解离能的影响. 计算结果表明, 用杂化泛函能得到与实验一致的优化几何构型和较合理的振动频率. 对Ni(CO)n(n=2~4)体系, 用“纯”泛函, 如BP86和BPW91, 可得到与CCSD(T)更符合、 并与实验值接近的解离能. 当解离产物出现单个金属原子或离子(如金属羰基配合物的完全解离)时, BSSE校正项的计算中应保持金属部分的电子结构一致. 只有考虑配体基组和不考虑配体基组两种情况下金属的电子构型与配合物中金属的构型一致时, 才能得到合理的BSSE校正, 从而预测合理的解离能.     

van der Waals corrections to density functional theory calculations: Methane,ethane, ethylene,benzene, formaldehyde,ammonia, water,PBE, and CPMD

Parameters are developed for a practical application of the empirical van der Waals (vdW) correction infrastructure available in the CPMD density functional theory (DFT) code. The binding energy, geometry, and potential energy surface (PES) are examined for methane, ethane, ethylene, formaldehyde, ammonia, three benzene dimer geometries, and three benzene–water geometries. The vdW corrected results compare favorably with MP2 and CCSD(T) calculations near the complete basis set limits, and with experimental results where they are available.     

SAMPL6 host–guest challenge: binding free energies via a multistep approach

In this effort in the SAMPL6 host–guest binding challenge, a combination of molecular dynamics and quantum mechanical methods were used to blindly predict the host–guest binding free energies of a series of cucurbit[8]uril (CB8), octa-acid (OA), and tetramethyl octa-acid (TEMOA) hosts bound to various guest molecules in aqueous solution. Poses for host–guest systems were generated via molecular dynamics (MD) simulations and clustering analyses. The binding free energies for the structures obtained via cluster analyses of MD trajectories were calculated using the MMPBSA method and density functional theory (DFT) with the inclusion of Grimme’s dispersion correction, an implicit solvation model to model the aqueous solution, and the resolution-of-the-identity (RI) approximation (MMPBSA, RI-B3PW91-D3, and RI-B3PW91, respectively). Among these three methods tested, the results for OA and TEMOA systems showed MMPBSA and RI-B3PW91-D3 methods can be used to qualitatively rank binding energies of small molecules with an overbinding by 7 and 37 kcal/mol respectively, and RI-B3PW91 gave the poorest quality results, indicating the importance of dispersion correction for the binding free energy calculations. Due to the complexity of the CB8 systems, all of the methods tested show poor correlation with the experimental results. Other quantum mechanical approaches used for the calculation of binding free energies included DFT without the RI approximation, utilizing truncated basis sets to reduce the computational cost (memory, disk space, CPU time), and a corrected dielectric constant to account for ionic strength within the implicit solvation model.     

Matrix-isolation FT-IR study and theoretical calculations of the vibrational, tautomeric and H-bonding properties of hypoxanthine

The neutral compound hypoxanthine is investigated using the technique of matrix-isolation FT-IR spectroscopy combined with density functional theory (DFT) and ab initio methods. Two theoretical methods (RHF and DFT/B3-LYP) are compared for vibrational frequency prediction, and four methods (RHF//RHF, MP2//RHF, DFT//DFT and MP2//DFT) for prediction of the relative energies of the tautomers and the interaction energies of the complexes. All the possible tautomeric forms have been considered theoretically, and the results indicate that two oxo forms (O17 and O19) and one hydroxy form (H9-r1) are the three most stable forms. The experimental FT-IR spectra are consistent with this prediction, and nearly all the characteristic spectral features of these forms have been identified in the spectrum. A theoretical study of the H-bonded complexes of these three tautomers with water is also performed. Several structures have been found for each form and the results demonstrate that the closed complexes with two H-bonds are the most stable systems due to the H-bond cooperative effect.     

An assessment of density functional methods for studying molecular adsorption in cluster models of zeolites

The performance of six density functional theory (DFT) methods has been tested for a zeolite cluster containing three tetrahedral atoms (3T) and the complexes it forms with water and methanol molecules. The DFT methods (BLYP, BP86, BPW91, B3LYP, B3P86, B3PW91) give results in good agreement with second-order perturbation theory (MP2). The results in this paper provide evidence of the suitability of DFT methods for studying hydrogen-bonded adsorption complexes in zeolites. Generally, the hybrid DFT methods are in closer agreement with experiment and MP2 than the pure DFT methods for geometrical parameters. The only exception is the Z⁻ geometry, perhaps due to its anionic character. All DFT methods give results in good overall agreement with MP2 for intramolecular geometrical parameters of the adsorption complexes, intramolecular vibrational frequencies, and adsorption energies. The B3LYP method gives intermolecular geometries and intermolecular vibrational frequencies which are closest to those obtained from the MP2 method. Thus, the B3LYP method seems to be the best choice for a density functional treatment of molecular adsorption in zeolite systems.