二十面体对称性(I~h)分子的从头计算研究II. 铜原子簇Cu~13的电子结构

应用对称性约化计算方案, 完成了铜原子簇Cu~13(I~h)三种基组下的从头计算, 最大维数390。为了进行比较, 也进行了Cu~2、Cu~4、Cu~6及Cu~8的计算。经过优化, 获得基态及平衡几何、布居、结合能等数据, 表明Cu~13可能稳定存在。Cu~13中以d成分为主的分子轨道均已填满, 对化学键无实际贡献, 成键作用为s, p性质; 再者, d带与s带不相交叠, 无金属Cu能带的特征。无论平衡几何、布居及结合能数值均与采用的其组很有关系, 虽然定性趋势是一致的。     

二十面体对称性(I~h)分子的从头计算研究II. 铜原子簇Cu~13的电子结构

应用对称性约化计算方案, 完成了铜原子簇Cu~13(I~h)三种基组下的从头计算, 最大维数390。为了进行比较, 也进行了Cu~2、Cu~4、Cu~6及Cu~8的计算。经过优化, 获得基态及平衡几何、布居、结合能等数据, 表明Cu~13可能稳定存在。Cu~13中以d成分为主的分子轨道均已填满, 对化学键无实际贡献, 成键作用为s, p性质; 再者, d带与s带不相交叠, 无金属Cu能带的特征。无论平衡几何、布居及结合能数值均与采用的其组很有关系, 虽然定性趋势是一致的。     

二十面体对称性(I_h)分子的从头计算研究 Ⅱ.铜原子簇Cu_(13)的电子结构

应用对称性约化计算方案,完成了铜原子簇Cu_(13)(I_h)三种基组下的从头计算,最大维数390.为了进行比较,也进行了Cu_2、Cu_4、Cu_6及Cu_8的计算.经过优化,获得基态及平衡几何、布居、结合能等数据,表明Cu_(13)可能稳定存在.Cu_(13)中以d成分为主的分子轨道均已填满,对化学键无实际贡献,成键作用为s,p性质;再者,d带与s带不相交叠,无金属Cu能带的特征.无论平衡几何、布居及结合能数值均与采用的基组很有关系,虽然定性趋势是一致的.     

双原子镧系化合物分子结构

利用相对论小芯赝势及新近优化得到的镧系元素的(14s13p10d8f6g)/ [6s6p5d4f3g] 价电子基组, 对双原子镧系化合物(LaH, LaO, LaF, EuH, EuO, EuF, EuS, GdO, GdF, GdH, YbH, YbO, YbF, YbS, LuH, LuO, LuF)的分子结构进行了计算. 除YbO, LuF分子外,其他分子的计算结果与现有实验值符合得很好. 对YbO分子, 在基态存在复杂的组态混合情况, 由于计算方法(CI(SD))的局限性, 导致理论值与实验值有较大差别. 对LuF分子, 则很可能从实验得到的分子结合能估计值太低了.     

原子轨道能级与核外电子排布

原子结构理论是现代化学的基础理论之一。但仍有许多问题,诸如:原子轨道和轨道能的概念、轨道能级高低次序、轨道的“填实”顺序和电离顺序、原子基态时核外电子排布及其与元素周期系的关系等,在化学教学中是经常遇到的。     

镧系水合离子的密度泛函理论研究

用密度泛函理论(DFT)方法研究了镧系水合离子[Ln(H2O9)]^3+(Ln=Ce,Pr,Nd,Pm,Ho,Er,Tm,Yb)的几何构型、电荷分布和Ln^3+与水的结合能,计算结果与实验基本符合,表明DFT方法也适用于计算镧系离子与中性配体形成的化合物,对计算结果的分析表明,Ln^3+与H2O之间主要通过Ln5d轨道与氧孤对电子相互作用成键而结合,其余轨道起的作用比较小,用镧系化合物成键模型解释了镧系离子与水的结合能从La到Lu逐渐增加的事实。     

吸热型金属合金化对钒基贮氢材料性能的影响

利用电荷自洽离散变分Xα(SCC-DV-Xα)方法计算了吸热型金属合金化对钒基贮氢材料性能的影响。研究表明：在V₆₃H₆₄中加入吸热型金属Cr、Mn、Ni后，随着原子序数的增加，V₅₁M₁₂H₆₄中H的净电荷依次逐渐增加，V的净电荷逐渐减小；氢化物V₅₁M₁₂H₆₄中V-H之间的离子性相互作用逐渐减弱，共价性相互作用逐渐增强；V-H之间的相互作用主要是V-4s和H-1s、H-2s轨道之间的相互作用。研究还表明材料放氢的平衡压力与其费米能有很好的线性关系，加入吸热型金属后，导致氢化物V₅₁M₁₂H₆₄中费米能增加，氢化物更不稳定，从而改善材料的吸放氢性能。     

希土冠醚配合物的电子结构

本文用INDO方法计算了希土冠醚配合物的分子构型、电子结构、电荷分布和键级,讨论了配位前后电荷分布特征,以及由于配位引起L→L_n电荷转移跟配合物电子结合能化学位移和配位活化的关系,解释了因冠醚内腔不同希土冠醚配合物呈现不同构型的内在原因。希土冠醚配合物的占据分子轨道以配位体轨道成分为主体(4f轨道除外),低空轨道以希土原子轨道成分为主体。其占据分子轨道可分为六组。冠醚环上引入苯环后配合物前线轨道呈现π键性质。其价键的主要贡献部份是5d轨道,其次是6p和6s。4f轨道基本上不参与成键。讨论了配合物的化学键性质及高配位数时稳定的因素。     

从头计算法分子轨道绘图程序

在前文中,我们报道了以Slater函数(STO)和类氢函数为原子轨道基组的分子轨道绘图程序,文介绍以Gauss函数(GTO)为基组的从头计算分子轨道绘图程序,该程序可绘制各类型(s,p,d等)GTO表示的原子轨道和以STO-GTO系基组构成的各种分子轨道ψ或|ψ|²的截面立体图及等值图,利用从头计算的结果,所绘制的图形能很好的反映从头计算法本身的特点。     

铜锌金属天然酶活性中心量子化学计算

以菠菜叶中天然超氧化物歧化酶（SOD）铜锌活性中心及人为去掉金属锌的活 性中心为模板，运用Gaussian 94量子化学程序，在B3LYP/LANL2DZ基组水平上进行 了计算，获得了分子轨道能量、电荷分布以及原子轨道对前沿分子轨道贡献的信息 。结果表明，金属铜对于催化歧化超氧阴离子O_2~-具有至关重要的作用，而金属 锌起到稳定结构和促成构建活性中心的作用。     

Pseudopotential study of the rare earth monohydrides,monoxides and monofluorides

Nonrelativistic and quasirelativistic energy-adjusted pseudopotentials for fixed 4f subconfigurations of the rare earth elements La through Lu together with corresponding optimized valence basis sets have been used in SCF and CI(SD) calculations to determine the spectroscopic constants for the energetically low lying superconfigurations of the lanthanide monohydrides, monoxides and monofluorides. The experimentally observed trends in dissociation energies, bond lengths and vibrational frequencies for the ground states of the calculated superconfigurations of the monoxides and monofluorides are well reproduced. The results for the monohydrides are mainly predictions.     

Effect of beta-ring rotation on the structures and vibrational spectra of beta-carotene: density functional theory analysis

The effect of beta-ring rotation on the structures and vibrational spectroscopic characteristics of beta-carotene, including infrared (IR) intensities and Raman activities, is analyzed using density functional theory. Two stable isomers having Ci symmetry are obtained. The reversion of bond lengths is ascribed to the hyperconjugation effect. The natural bond orbital (NBO) charge analysis suggests that the NBO charges of C5 can be used to estimate the degree of pi-electron delocalization. These structural variations are used to analyze and assign the vibrational spectra. It is concluded that (a) the similar rotational angle dependencies of nu1 and nu2 frequencies justify the contribution of C=C stretch vibrations to the nu2 mode and explain the same conjugation length dependencies of nu1 and nu2 frequencies in polyenes, (b) the nu1 mode can be assigned to the C=C stretching in the central part of polyene chain, whereas beta-rings play an important role in nu2 and IR1 bands, especially for the all-trans isomer, and (c) the transition dipole moment of the calculated IR1 absorption band is relevant to the conjugation degree and the crossing angle between the eigenvectors of the polyene chain and the C5=C6 stretching vibration. This theoretical analysis, together with our previous Raman spectral experiments, suggests that the C6-C7 bond is easier to be twisted than other parts of beta-carotene molecule and so provides an insight into the structures of carotenoids and the properties of binding sites in carotenoproteins.     

Insight of the Structures and Properties on 2-Thioxanthine Complexes with One Hg~(2+) and Two Cl~- Ions:a Theoretical Investigation

The molecular structures of fifteen possible 2-thioxanthine(2TX) complexes with one Hg~(2+) and two Cl-ions were fully optimized using density functional theory B3PW91/6-311++G** method. The effective pseudo potential LANL2DZ basis set was used for metal Hg~(2+)ion. The vibrational analysis was also carried out at the same level. The bond lengths, bond angles, zero point energies, Gibbs free energies, thermodynamic energies and relative energies of all the complexes were obtained. The NBO analysis for natural charge and the second order perturbation energy values was carried out for three stable complexes and the IR spectroscopy of the two complexes was assigned to the experimental data. The results show that the 2-thioxanthine complexes with one Hg~(2+) and two Cl-ions were formed and the complexes resulting from the thione tautomer are more stable than that of the thiol ones. The order of three complexes with relative lower energy is 2TX(1,3,7)-Hg~(2+)-2, 2 TX(1,3,7)-Hg~(2+)-1 and 2 TX(1,3,9)-Hg~(2+). The calculated IR spectroscopy of the two complexes agreed with the experimental data.     

Study of hydrogen-bonded clusters of 2-methoxyphenol–water

Various hydrogen-bonded clusters of 2-methoxyphenol (2MP) with water have been analyzed using ab initio methods and Atoms in Molecules (AIM) theory. The intramolecular hydrogen bond energy (and enthalpy) for 2MP was evaluated from two different methods. The results of rotational barriers method are in better agreement with experimental data. Binding energies, vibrational frequencies and geometrical parameters were examined and compared for these complexes. It was shown that in the most stable complex, water acts both as a donor and an acceptor. The “bifurcated” complex was shown to be relatively stable based on energy values. Atoms in Molecules and Natural Bond Orbital (NBO) analysis were used to confirm the existence of hydrogen bonds and to compare the strengths of them. The results obtained from quantum mechanical, AIM and NBO calculations are in agreement with each other.     

Molecular structure, vibrational spectra and NBO analysis of phenylisothiocyanate by density functional method

The molecular geometry, vibrational frequencies and NBO analysis of phenylisothiocyanate (PITC) in the ground state have been calculated by using density functional theory calculation (B3LYP) with 6-311++G(d,p) basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with experimental values. Comparison of the observed fundamental vibrational frequencies of the PITC and calculated result by density functional theory (B3LYP) indicates B3LYP is superior for molecular vibrational problems. The entropy of the title compound was also performed at HF/B3LYP/6-311++G(d,p) levels of theory. Natural bond orbital (NBO) analysis of title molecule is also carried out. A detailed interpretation of the IR and Raman spectra of PITC is reported on the basis of the calculated potential energy distribution (PED). The theoretical spectrogram for IR spectrum of the title molecule has been constructed.     

A DFT study on the geometry,spectroscopic properties,and tautomerization of the local anaesthetic drug prilocaine

The prilocaine is a significant amino amide local anaesthetic. This drug can exist as three possible tautomers. Herein, by using density functional theory (DFT), and handling the solvent effects with the PCM model, the structure, energetic behavior, kinetics and mechanism of tautomerization, as well as the natural bond orbital analysis (NBO) of the prilocaine are reported. P1 is the most stable tautomer of the prilocaine, which can be tautomerized to two other tautomers via the intramolecular-proton transfer. Good agreement between the calculated NMR chemical shifts and IR vibrational frequencies with the experimental values approves the suitability of the optimized geometry for the prilocaine. A large HOMO-LUMO energy gap implies a high stability of the prilocaine.     

Energy of Chemical Bonds in Lanthanide Hydrides

The results of calculations of the energy of chemical bonds in lanthanide hydrides LnH _x (x = 1, 2, and 2 < x 3) are presented. Data for gaseous monohydrides have been predicted. A decrease in the bond energy of LaH with an increase in the coordination number of La in crystalline hydrides was demonstrated. The data, obtained for the first time within the framework of the structural thermodynamic model, were compared to the results of LCAO MO calculations.     

Theoretical Study on the Intermolecular Interactions of Tetrazole Dimers

1 INTRODUCTION Tetrazole and its derivatives are widely applied in the fields of agriculture, biology, chemistry, phar- macology and photographic technology, and they play significant roles in the science and technology as well as national defence[1]. In the past, the res- earches were focused on the molecular geometries, electronic structures, IR, thermodynamic properties, tautomerization, pyrogenation and sensitivity of tetrazole compounds[1～5]. However, study of tetra- zole dimers ha…     

Tautomerism of the antiepileptic drug Felbamate: A DFT study

The Felbamate is a novel anticonvulsant and neuropathic pain drug that can exist as three possible tautomers. Herein, employing density functional theory (DFT) and handling the solvent effects with the PCM model, the structural parameters, energy behavior, natural bond orbital analysis (NBO), as well as the tautomerism of Felbamate are investigated. F1 is the kinetically and thermodynamically most stable tautomer of Felbamate, which contains the amide group in each of the carbamate moieties. The calculated NMR chemical shifts and IR vibrational frequencies are in good agreement with the experimental values, confirming the suitability of the optimized geometry for Felbamate. The tautomerization reaction of F1 to each of the other tautomers occurs via an intramolecular proton transfer. This reaction affects considerably the structural parameters and atomic charges of the Felbamate molecule. A large HOMO-LUMO energy gap implies a high stability of the F1 tautomer.     

Density functional theory calculations and vibrational spectral analysis of 3,5-(dinitrobenzoic acid)

The FT-IR and Raman spectra of 3,5-dinitrobenzoic acid (DNBA) have been recorded and analyzed. The equilibrium geometry, various bonding and harmonic vibrational wavenumbers have been calculated with the help of density functional theory (DFT) method. Most of the vibrational modes are observed in the expected range. Mulliken population analysis shows the interactions C-N-O?H-C and C-O?H-C. The most possible interaction is explained using natural bond orbital (NBO) analysis. The strengthening and polarization of the CO bond increases due to the degree of conjugation. HOMO-LUMO energy and the thermodynamic properties are also evaluated.