四氢吡咯双自由基及其等电子体系不同电子态稳定性和NLO性质的理论研究

摘要所选体系为非路易斯分子,即分子中含有一个可分裂的C—C键,两个电子占据非键分子轨道,对这类分子的能量和稳定性的研究已有报道．根据体系中两个自由基电子相互作用不同,该类分子可能具有三种电子态．本文采用密度泛函和从头算等方法在不同基组水平上,对四氢吡咯双自由基（体系a）及其两个等电子体系的NLO性质进行了理论研究．采用不同方法和基组优化体系a三种电子态的几何结构,     

MO_2分子基态的全活化空间多组态自洽场研究(英文)

近些年来，对过渡金属簇，特别是二聚物的电子结构及光谱性质的研究已成为化学家们非常关心的一个课题，因为这方面的研究能使人们对过渡金属多重键的本质及d轨道在成键中的作用有一个深入的了解和认识．这无论是对配位化学，还是对于材料科学，都有着十分重要的意义．采用全活化空间多组态自洽场方法，对Mo2分子基态的电子结构、光谱性质及势能曲线进行了相对论有效势从头算研究，得出了较为合理的结果,根据计算预测Mo─Mo多重键的键级为4．95．     

高精度的非相对论与完全相对论密度泛函理论计算方法和程序

介绍非相对论与完全相对论密度泛函理论计算方法和相应的计算程序（ＮＲ／Ｒ－ＤＦＴ）的结构和功能。本程序是目前用密度泛函理论方法计算完全相对论总能量能达到最高精度的程序。利用本程序可以高精度地计算含重元素体系的总能量、分子轨道能级、原子化能、键合能、偶极矩，分析化学键性质等。     

局域和长程杂化密度泛函研究推拉结构有机发光分子

用含时密度泛函方法研究了具有推拉结构的有机发光材料3-(二氰亚甲基)-5,5-二甲基-1-(4-[9-咔唑基]-苯乙烯基)环己烯(DCDCC)的吸收和荧光光谱, 并考虑了溶剂效应. 通过与实验光谱的比较, 重点评价了包括局域和长程在内的8种交换泛函. 结果表明泛函的选择对结果的可靠性至关重要, 在密度泛函和含时密度泛函理论框架下, 包含44% Hartree Fock交换泛函的BMK杂化函数联同连续极化模型和中等大小的基组最适合研究DCDCC分子的光谱性质. 此外, 尽管DCDCC分子内电荷转移并没有强致发出双荧光, 但仍然可以用平面分子内电荷转移和扭转分子内电荷转移模型解释DCDCC激发态的结构. BMK泛函计算的结果表明DCDCC的激发态结构支持平面分子内电荷转移模型.     

镱硫属化合物的密度泛函理论研究

用密度泛函理论(DFT)研究镱硫属化合物的电子结构和性质,通过与实验比较考察了现有的几种近似密度泛函公式对镧系元素化合物的适用程度和相对论效应的影响.结果表明,用DFT计算的YbO键长对实验值的偏差约为0.002nm;但得到的键能即使在考虑梯度校正和相对论效应之后,仍比实验值高,在定域密度近似基础上引入交换梯度校正使键能计算值减小,其中PW86x使键能计算值减小稍多些,结果更接近实验值;相关梯度校正使键能计算值升高.相对论效应使键长缩短0.004～0.006nm,键能减小约0.5eV.计算结果的分析表明,Yb的5d轨道和配体的np轨道间形成σ键和π键.在所研究的分子体系中,配体原子从O到Te、Yb原子的5d轨道布后数依次减少,同键能减弱的顺序一致.相对论效应使键能减小的主要原因是在成键过程中发生了Yb的6s电子向5d轨道的转移,而相对论效应使该过程能量增加.偶极矩和电荷分布的计算表明,Yb-L键以共价性为主,相对论效应使共价性成份增加.     

Ni(110)-p2mg(2×1)-CO表面的几何结构和电子态

利用密度泛函理论(DFT)总能计算研究了Ni(110)-p2mg(2×1)-CO表面的原子结构和电子态. 计算结果表明: CO分子吸附于该表面的短桥位附近, 分子吸附能为1.753 eV, CO分子的键长dC—O为0.117 nm, 分子与表面竖直方向的夹角为20.0°, 碳原子和短桥位中点的连线与竖直方向的夹角为20.9°; 吸附的CO分子内原子间的伸缩振动频率为1876和1803 cm-1. 态密度研究结果表明吸附作用主要来自CO分子π、σ轨道与衬底d轨道间的杂化作用. CO分子σ轨道和衬底表面镍原子dxz轨道杂化形成的表面电子态主要位于费米能以下-10.4 至-8.8 eV和-7.4至-5.1 eV 范围内. σ和dxz轨道间的杂化作用可能是形成p2mg表面对称性的重要因素之一.     

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％.     

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（XYG3typeofdoublyhybrid,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．     

等电子三原子铀化物OUO2+、NUN和NUO+的结构和谐振频率的CCSD(T)计算研究

用小核相对论有效势和CCSD(T)方法计算了三原子铀化物OUO²⁺, NUN和NUO⁺的平衡键长和谐振频率. 计算结果显示U原子内层5s5p5d 电子相关能对这些化合物性质的影响非常小. 除NUN的弯曲振动频率,旋轨耦合效应对这些化合物的结构和频率的影响并不明显. 本文的计算结果与其他研究组的计算结果以及已有的实验值相比符合较好, 这表明作为单参考态方法, CCSD(T)能够对这些体系的键长和频率给出较精确的计算结果. 与此前密度泛函理论(DFT)的计算结果相比, CCSD(T)方法与PBE0泛函的结果吻合最好. 本文的工作有助于在用密度泛函方法研究这些体系时选择合适的交换相关泛函, 也为今后的实验研究提供了新的理论数据.     

量子化学计算预测高效液相色谱键合相的保留机理

本文用Gaussian98计算软件中的Hartree—Fock方法对高效液相色谱中溶质与固定相发生作用后产生的能量进行计算,并对溶质与C18键合相和苯胺甲基键合相相互作用的计算结果与实验结论进行了比较。结果表明,量化计算结果与色谱保留行为之间具有相关性,即分子间相互作用能量的高低,决定了保留值的大小,表现为能量越负,保留值越大,而且双倍键合量的能量低于单倍键合量。量化计算的方法将为色谱保留性能的研究和键合相的研制提供参考。     

Density functional investigations of the properties and thermochemistry of UF6 and UF5 using valence-electron and all-electron approaches

The structural properties and thermochemistry of UF6 and UF5 have been investigated using both Hartree-Fock and density functional theory (DFT) approximations. Within the latter approach, the local spin-density approximation, the generalized gradient approximation, and hybrid density functionals were considered. To describe the uranium atom we employed small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (RECPs), as well as the all-electron approximation based on the two-component third-order Douglas-Kroll-Hess Hamiltonian. For structural properties, we obtained very good agreement with experiment with DFT and both large and small-core RECPs. The best match with experiment is given by the hybrid functionals with the small-core RECP. The bond dissociation energy (BDE) was obtained from the relative energies of the fragments [UF6 --> UF5 + F], corrected for zero-point energy and spin-orbit interaction. Very good agreement was found between the BDE obtained from all-electron calculations and those calculated with the small-core RECP, while those from the large-core RECP are off by more than 50%. In order to obtain good agreement with experiment in the BDE it is imperative to work with hybrid density functionals and a small-core RECP.     

Density functional and Ab initio study of Cr(CO)n (n = 1-6) complexes

Cr(CO)n (n = 1-6) systems were studied for all possible spin states using density functional and high-level ab initio methods to provide a more complete theoretical understanding of the structure of species that may form during ligand dissociation of Cr(CO)6. We carried out geometry optimizations for each system and obtained vibrational frequencies, sequential bond dissociation energies (BDE), and total CO binding energies. We also compared the performance of various DFT functionals. Generally, the ground states of Cr(CO)6, Cr(CO)5, and Cr(CO)4, whose spin multiplicity is a singlet, are in good agreement with both previous theoretical results and currently available experimental data. Calculations on Cr(CO)3, Cr(CO)2, and CrCO provide new findings that the ground state of Cr(CO)3 might be a quintet with C2v symmetry instead of a singlet with C3v symmetry, and the ground state of Cr(CO)2 is not a linear quintet, as suggested by previous DFT calculations, but rather a linear septet. We also found that nonet states of Cr(CO)2 and CrCO display partial C-O bond breakage.     

The confirmation of accurate combination of functional and basis set for transition‐metal dimers: Fe2, Co2, Ni2, Ru2, Rh2, Pd2, Os2, Ir2, and Pt2

Eight kinds of density functionals named B3LYP, PBE1PBE, B1B95, BLYP, BP86, G96PW91, mPWPW91, and SVWN along with two different valence basis sets (LANL2DZ and CEP‐121g) are employed to study the transition‐metal dimers for the elements of group VIII. By comparing the equilibrium bond distances, vibrational frequencies, and dissociation energies of the ground state of these dimers with the available experimental values and theoretical data, we show that the “pure” DFT methods (G96PW91, BLYP, and BP86) with great‐gradient approximation always give better results relative to the hybrid HF/DFT schemes (B3LYP, PBE1PBE, and B1B95). The striking case found by us is that the G96PW91 functional, which is not tested in previous systemic studies, always predicts the dissociation energy to be well. The Ru₂ and Os₂ dimers are sensitive to not only the functionals employed but also the valence basis sets adopted. The natural bond orbital population is analyzed, and the molecular orbitals of the unpaired electrons are determined. Furthermore, our results indicate that the s and d orbitals of these dimers always hybridize with each other except for Rh₂ and Pt₂ molecules. And by analyzing the electron configuration of the bonding atom, the dissociation limit of the ground state is obtained. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Density functional and multiconfigurational ab initio study of the ground and excited states of Os2

Multiconfigurational ab initio methods predict that the ⁵Π_u state as the ground state instead of the ⁷Δ_u state. Although multiconfigurational perturbation theory correctly predicts the ground state, they overestimate the bond dissociation energy (BDE). Only multireference configuration interaction method can reasonably calculate the BDE. The spin‐orbit effect on the spectroscopic constants is not significant. The results calculated by density functional theory (DFT) vary significantly depending on the selection of a DFT functional. No DFT functional gives the same energy ordering as calculated by the second‐order multiconfigurational perturbation theory (CASPT2). The old generalized gradient approximations functionals are well suited for predicting the ground state and calculating the bond length and the vibrational frequency of Os₂. According to the CASPT2 calculation, the ground state of Os₂ has a quadruple bond. © 2014 Wiley Periodicals, Inc.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

Density functional and spin-orbit ab initio study of CF3Br: molecular properties and electronic curve crossing

Quantum chemical calculations of CF(3)Br and the CF(3) radical are performed using density functional theory (DFT) and time-dependent DFT (TDDFT). Molecular structures, vibrational frequencies, dipole moment, bond dissociation energy, and vertical excitation energies of CF(3)Br are calculated and compared with available experimental results. The performance of six hybrid and five hybrid meta functionals in DFT and TDDFT calculations are evaluated. The ωB97X, B3PW91, and M05-2X functionals give very good results for molecular structures, vibrational frequencies, and vertical excitation energies, respectively. The ωB97X functional calculates well the dipole moment of CF(3)Br. B3LYP, one of the most widely used functionals, does not perform well for calculations of the C-Br bond length, bond dissociation energy, and vertical excitation energies. Potential energy curves of the low-lying excited states of CF(3)Br are obtained using the multiconfigurational spin-orbit ab initio method. The crossing point between 2A(1) and 3E states is located near the C-Br bond length of 2.45 ?. Comparison with CH(3)Br shows that fluorination does not alter the location of the crossing point. The relation between the calculated potential energy curves and recent experimental result is briefly discussed.     

A density functional study of chemical reactions

Density functional theory (DFT ) was used to study reactions involving small molecules. Relative energies of isomers and transition structures of diazene, formaldehyde, and methylenimine were determined using various DFT functionals and results were compared with MP 2 and MP 4 calculations. DFT reaction barriers were found to be consistently lower. For some reactions, such as OH + H₂→ H₂O + H, gradient-corrected functionals predict very low or nonexistent barriers. The hybrid Hartree–Fock–DFT adiabatic connection method (ACM ) often provides much better results in such cases. The performance of several density functionals, including ACM , was tested in calculations on over 100 atomization, hydrogenation, bond dissociation, and isodesmic reactions. The ACM functional provides consistently better geometries and reaction energetics than does any other functional studied. In cases where both HF and gradient-corrected DFT methods underestimate bond distances, the ACM geometries may be inferior to those predicted by gradient-corrected DFT methods. © 1995 John Wiley & Sons, Inc.     

Density functional study of AuXq (X = O, S, Se, Te, q = +1, 0, -1) molecules

Bond distances, vibrational frequencies, electron affinity, ionization potential, and dissociation energies of the title molecules were studied by use of density functional methods B3LYP, B3P86, B3PW91, BHLYP, BLYP, BP86, mPW1PW91, and PBE1PBE. It was found that the ground electronic state is doublet for neutral species, singlet for the anion, and triplet for the cation, in agreement with experiments and previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. The predicted bond distances and vibrational frequencies are in agreement with experiments and previous theoretical results. BP86 and BLYP have relatively good performance in reproducing the experimental results, while BHLYP is the worst functional method compared with the other density functional methods used for the title molecules.     

Phenol O–H bond dissociation energy in water clusters

We are reporting ab initio and density functional theory (DFT) calculations for the phenol O–H bond dissociation energy in the gas phase and in phenol–water clusters. We have tested a series of recently proposed functionals and verified that DFT systematically underestimates the O–H bond dissociation energy of phenol. However, O–H bond dissociation energies in water clusters are in reasonable agreement with experimental data for phenol in solution. We have evaluated electronic difference densities in phenol–water, phenoxy–water, and water, and we are suggesting that the representation of this quantity gives an interesting picture of the electronic density rearrangement induced by hydrogen bond interactions in phenol–water clusters. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Configuration interaction based on constrained density functional theory: a multireference method

Existing density functional theory (DFT) methods are typically very effective in capturing dynamic correlation, but run into difficulty treating near-degenerate systems where static correlation becomes important. In this work, we propose a configuration interaction (CI) method that allows one to use a multireference approach to treat static correlation but incorporates DFT's efficacy for the dynamic part as well. The new technique uses localized charge or spin states built by a constrained DFT approach to construct an active space in which the effective Hamiltonian matrix is built. These local configurations have significantly less static correlation compared to their delocalized counterparts and possess an essentially constant amount of self-interaction error. Thus their energies can be reliably calculated by DFT with existing functionals. Using a small number of local configurations as different references in the active space, a simple CI step is then able to recover the static correlation missing from the localized states. Practical issues of choosing configurations and adjusting constraint values are discussed, employing as examples the ground state dissociation curves of H(2) (+), H(2), and LiF. Excellent results are obtained for these curves at all interatomic distances, which is a strong indication that this method can be used to accurately describe bond breaking and forming processes.