富勒烯C60的柱色谱分离法研究

本文提出了由Ｃ（６０）、Ｃ（７０）及少量高级富勒烯混合物（来自电弧汽化石墨所形成的碳灰）中分离出纯度为９９．９％Ｃ（６０）的两种改进的、简便价廉的柱色谱分离法．第一种方法用中性氧化铝作固定机以石油醚与甲苯（Ｖ／Ｖ＝９２．５／７．５）混合液作流动相；另一种方法以活性炭与硅胶作固定相，以甲苯作流动相，柱顶氮压约为０．０１ａｔｍ．本文尚将这两种方法与文献报道的两种相近的方法分别进行了比较．     

H8Si8O12和H8Si7TiO12 团簇的几何构型和电子结构的从头算研究

应用HF、 MP2和杂化的B3LYP方法,使用3-21G基组,对H8Si8O12 和H8Si7TiO12团簇的几何构型、总能进行了计算,并在B3LYP/3-21G的水平上对硅原子的核磁共振化学位移进行了研究,得到的几何构型,以及核磁共振化学位移与实验结果进行了比较,发现吻合得很好。计算了H8Si8O12和H8Si7TiO12团簇的Mulliken布居数的大小。并对Si原子被Ti原子取代前后的H8Si8O12体系的几何构型、 Mulliken布居数的变化进行了比较和研究。     

精密从头算与ABEEM／MM模型对水团簇（H2O）11 9种低能结构的计算

用精密从头算方法研究了(H2O)11的9种低能异构体的性质,包括优化的几何结构、结合能、偶极矩和氢键个数等,并且得出了515-a是(H2O)11的全局最低能结构.同时,也用ABEEM/MM(atom bond electronegativity equalization method/molecular mechanics)模型研究了这些性质,与从头算的结果进行了比较,得到了相符合的结果.这显示了ABEEM/MM模型在描述中等大小的水分子团簇结构上是成功的.     

N_2H_4-CH_3OH氢键团簇体系的从头计算

用从头计算法研究了 (N2 H4-CH3OH)氢键团簇体系。分别在HF/6 31G 和HF/6 31G 水平上对它们的中性和离子团簇进行几何全优化 ,得到了 3种中性混合团簇稳定构型和离子混合团簇稳定构型 ,并对其能量和稳定性进行了比较。讨论了 3种不同构型离子团簇可能的解离通道。给出了质子化混合团簇的稳定构型 ,并对其可能的解离通道进行了讨论。文中最后计算出N2 H4,CH3OH ,(N2 H4-CH3OH)团簇的质子亲和能 (PA) ,分别为 :2 0 6.7kcal/mol,1 78.3kcal/mol,2 2 7.5kcal/mol,其中质子亲和能PAcalc[N2 H4]与实验值PAexp[N2 H4]=2 0 4 .8kcal/mol符合得很好。     

精密从头算与ABEEM/MM模型对水团簇(H2O)11 9种低能结构的计算

用精密从头算方法研究了(H2O)11的9种低能异构体的性质, 包括优化的几何结构、结合能、偶极矩和氢键个数等, 并且得出了515-a是(H2O)11的全局最低能结构. 同时, 也用ABEEM/MM(atom bond electronegativity equalization method/molecular mechanics) 模型研究了这些性质, 与从头算的结果进行了比较, 得到了相符合的结果. 这显示了ABEEM/MM模型在描述中等大小的水分子团簇结构上是成功的.     

1,4-二氧六环和氨分子氢键团簇的从头算

在不同基组水平上,对１,４－二氧六环和氨分子氢键团簇体系进行了从头算分子转道法研究,优化得到中性团簇,离子团簇和碎片离子（质子化团簇离子和非质子化团簇离子）平衡几何构型,研究结果表明：中性团簇最稳定构型为Ｒ－ＨＮ２－ＨＮＮ２（Ｒ：１,４－二氧六环）,离子团簇由于发生质子转移,其构型与中 团簇有较大的淡同,两类碎片离子Ｒ（ＮＨ３）＋和Ｒ（ＮＨ３）Ｈ＾＋与中性团簇Ｒ（ＮＨ３）的结构也有所不同     

富勒烯[60]的光化学反应研究

从光物理出发,综述了近几年富勒烯「６０」的光化学反应研究进展。Ｃ６０能发生诸多的光化学反应：（１）光氧化;（２）光氢化还原;（３）「２＋２」光环化加成;（４）与叔胺的光加成;（５）与氨基酸的光加成;（６）与金属有机化合物的光加成。     

Pd2—CO簇的从头算研究

采用带相地论赝势的金属态原子基组，对Ｐｄ２－ＣＯ簇进行了从头算研究，按金属态原则和键态原则，计算ＣＯＤ 金属钯表面桥位吸附模型，并讨论吸附作用的化学键本质，认为将Ｐｄ２的前线轨道中占据的（５ｓ＋５ｓ）轨道的电子激发到空的（５ｓ－５ｓ）轨道，是其吸附作用的键准备态，此态既减少了Ｐｄ２（５ｓ＋５ｓ）轨道与ＣＯ的５σ之间的排斥，又有利于Ｐｄ２（５ｓ－５ｓ）轨道与ＣＯ的２π的π反馈。     

甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.     

六氢吡啶和氨形成的氢键团簇C5H10NH(NH3)n(n=1～3)结构的从头算研究

在RHF/6-31G(d)水平下,对C5H10NH(NH3)n(n=1～3)氢键团簇的平衡构型进行了从头算研究,优化得到各种可能的平衡构型.C5H10NH(NH3)为线型氢键结构,而C5H10NH(NH3)2为三元环结构,C5H10NH(NH3)3为四元环结构.在MP2/6-31G(d)//B3LYP/6-31G(d)水平下,对最稳定构型C5H10NH(NH3)n(Ⅰ)(n=1～3)的分子轨道进行布居分析,并且对相应的占据轨道进行指认.C5H10NH(NH3)n(Ⅰ)(n=1～3)垂直电离势的计算结果表明,形成氢键团簇后,分子的垂直电离势降低.     

Ab initio analysis of the interaction of CO2 with acetylated d-glucopyranose derivatives

Peracetylated d-glucopyranose has a high solubility in CO₂ and can be a promising phase-change physical solvent or absorbent for CO₂, as reported recently. However, peracetylated d-glucopyranose is unstable under acidic atmospheres, especially in sulfur-containing waste gases, and the possibly major decomposition products are 2,3,4,6-tetra-O-acetyl-d-glucopyranose, 1-thiol-d-glucopyranose tetraacetate, and 1-mercaptoethyl-d-glucopyranose tetraacetate. Therefore, it is highly interesting to investigate the interaction between CO₂ and these three compounds using ab initio calculations, including geometry optimizations with HF/3-21G, B3LYP/6-31+G** and single-point energy calibration with MP2/aug-cc-pVDZ. The results indicate that the electrostatic interactions between the substrates and CO₂ are mainly influenced by the interaction distance and the numbers of negative charge donors or the interacting pairs involved in the complex. It is furthermore found that ΔE increases significantly if S and O atoms could interact with CO₂ simultaneously. The binding energy is irrelevant if one considers the chemical environment of the O atom (i.e. O_Ac, O_E or O_S) or the S atom (i.e. SEt or SH), and the electronegativity difference between the S and O atoms. The three substrates studied are still excellent CO₂-philes, although their average ΔE (–20 kJ/mol) is slightly lower than that of peracetylated d-glucose (–22 kJ/mol), which has one more O atom that can interact with CO₂. Therefore, the applications of carbohydrates can be expanded to include adsorbents for CO₂, SO₂ or both, and the functional groups attached to the carbohydrate can vary from those to the acetyl groups.     

CX_3NO(X=H,F,Cl)分子结构稳定性的Ab initio研究

CH_3NO(1)、CH_2FNO(2)、CHF_2NO(3)、CH_2ClNO(4)、CHCl_2NO(5)、CHCIFNO(6)、CF_3NO(7)和CCl_3NO(8)是一类重要的光化学分子,它们稳定性差、寿命短,实验研究其结构及稳定性较困难,仅CH_3NO、CF_3NO和CCl_3NO分子有理论研究,其余均未见报道,本文用ab initio方法在STO-3G水平上研究了上述分子结构稳定性,还用STO/     

Au(Ⅰ)电荷转移配合物光谱性质的从头算研究

过渡金属电荷转移配合物的电荷分离是光能转化为电能的光物理过程, 与配合物的电子结构密切相关. 采用从头算方法探索了双核Au(Ⅰ)配合物, cis-[Au2(SHCH2PH2)2]2+(1), cis-[Au2(SHCH2S)2](2) 和cis-[Au2(PH2CH2S)2](3)的电荷转移性质. 采用MP2计算得到基态的Au(Ⅰ)—Au(Ⅰ)距离分别为0.2972, 0.2888和0.2903 nm, 表明Au(Ⅰ)之间存在弱吸引作用; 电子激发使得配合物2和3的金属间的距离缩短了约0.016 nm, 而配合物1仅增长了0.002 nm. CIS方法预测配合物1~3的3A激发态分别产生383, 463和422 nm最低能发射, 具有金属中心(Metal-centered, MC)跃迁和分子内电荷转移(Intramolecular Charge Transfer, ICT)的混合性质.     

Ab initio calculations on the molecular structure of fluorocyanopolyynes

The molecular structure of the first three members of the fluorocyanopolyynes was studied by ab initio Hartree-Fock calculations with a polarized double zeta basis set and at MP2 level with the same basis set. Alternating triple and single bonds were found; a theoretical estimate of rotational constants and dipole moments was performed and a comparison with the available experimental data was made. An analysis of the theoretical vibrational frequencies of the title compounds was carried out.     

Ab initio studies of methylenecarbene and isoelectronic species

Optimum equilibrium geometries, energetics, harmonic vibrational frequencies, and infared intensities within the double harmonic approximation are computed for methylenecarbene, CCH₂, and isoelectronic species involving silicon and germanium at both the SCF level of theory and the level of second-order perturbation theory using a 6-311G(2df, 2p) basis set or its equivalent. Optimum equilibrium geometries and energetics are also computed at both levels of theory using a smaller 6-311G(d, p) basis set or its equivalent. This investigation of these species is the first to include all of the systems with germanium. In addition, this present work is the first study to includef-type polarization functions in a systematic investigation of the molecular structure and properties of all the molecules in the series. Acetylenic structures are also computed for energy comparisons. Of all the linear isomers, only acetylene is found to be a minimum on the potential energy surface. However, all of the C_2v structures are found to be local minima. Both the C_2v and linear structures will serve as a basis for future work involving mapping the entire hyperenergy surfaces of all of the molecular systems in the series.     

H2O在Cu(100)表面吸附的从头算研究

用量子化学从头计算方法,以原子簇Cu₅为模拟表面,研究了水在Cu(100)面上不同吸附位的吸附情况,结果表明:水分子通过氧原子与表面成键,顶位是其最佳吸附位,吸附能约为70kJ/mol,平衡距离为0.213nm,氢原子远离表面.在氧原子不加极化函数时,水分子的二次轴垂直于表面时能量最低,但倾斜至50°所需能量仅在10kJ/mol以内.当考虑O原子d轨道的影响时,水分子倾斜时能量较低,得到了与实验相符的吸附构型.另外还研究了表面电荷对吸附体系的影响,结果表明:表面带正电荷时,水与表面间的相互作用增强,水上所转移电荷增多,Cu-O间平衡距离减小;表面带负电荷时,情况与之相反,且氢原子靠近表面时,势能曲线有最低点.     

Benzooxirene. Ab initio calculations

Ab initio calculations have been performed on benzooxirene, the corresponding oxo carbene (“ketocarbene”), and the transition state linking the two. At the highest level used, QCISD(T)/6-31G^*//MP2(FULL)/6-1G^* with MP2(FULL)/ 6-31G^* zero point energy corrections, the relative energies of the oxirene, the transition state and the carbene are 0, 24.6, and −17.8 kJ mol⁻¹. Correlation energy effects are very important in this system: at the QCISD(T) level the oxirene lies above the carbene, as at the MP4 and HF levels, but at the MP2 level the ordering is reversed. Benzooxirene is probably slightly nonplanar: the HF/6-31G^* geometry is C_2v but the MP2(Fermi contact)/6-31G^* geometry is C_s with a 6-/3-ring coplanarity deviation of about 6.9 °, although in the MP2(FULL)/6-31G^* geometry this is reduced to about 3.1 °.     

Ab initio study of anomeric effect in 2,2-difluoroglycine

The optimized molecular structures of seven conformations of 2,2-difluoroglycine have been obtained from ab initio calculations. For conformers in which the lone pair of electrons on the nitrogen are antiperiplanar to one of the C–F bonds, that C–F bond is longer than the other C–F bond, which is synperiplanar to the lone pair of electrons. Conformers which have these features are the most stable conformers of those examined. This observation is explained in terms of an anomeric effect of the 1p(N)→σ^*(C–F). At the MP2/6-31G^* level of calculation, conformers IV and V are 21.5 and 18.7 kJ/mol, respectively, more stable than the least stable conformer, VI, which does not exhibit an anomeric effect. Conformer VII was found to be exceptionally stable, in addition to an anomeric effect, this conformer also exhibits features of a FH–O hydrogen bond.     

Ab initio interaction and spectral properties of CO+–He

In this contribution, ab initio methods have been used to study the open-shell CO⁺–He van der Waals (vdW) complex in both the ground and the first Π excited electronic state. Calculations were performed at the UCCSD(T) level of theory in the framework of the supermolecule approach using the cc-pVTZ basis set complemented with a set of standard bond functions in the middle of the vdW bond. Calculations predict a most-stable equilibrium conformation with β e=45°, R _e =2.85 Å and D _e =275 cm^?1 for the ground CO⁺(X²Σ)–He(¹S) state and β e=90°, R _e =2.70 Å and D _e =218 cm^?1 for the excited CO ⁺(A²Π)–He(¹S) state. The dipole moment μ and independent components of the field polarizability α of the CO ⁺–He vdW complex have been studied at the calculated equilibrium geometry of these states. The vertical excitation energies from the ground CO⁺(X ²Σ)–He(¹S) to the excited CO⁺(A²Π)–He (¹S) electronic state and corresponding shifts in the fluorescent spectrum with respect to the isolated CO⁺ molecule are also presented     

Structural transition of NaBH4 under high pressure: Ab initio calculations

The pressure induced structural transition of NaBH₄ from β-NaBH₄ (tetragonal-P42_1c) to γ-NaBH₄ (orthorhombic-Pnma) is investigated by ab initio plane-wave pseudopotential density functional theory method (DFT). The BaSO₄-type structure of orthorhombic high-pressure phase is testified theoretically for the first time. The calculated transition pressure of β-NaBH₄ (tetragonal-P42_1c) to γ-NaBH₄ (orthorhombic-Pnma) is 9.66 GPa and the orthorhombic high-pressure phase is stable up to 30 GPa. Our results agree well with previous experimental results and demonstrate that high-pressure phase transition from β-NaBH₄ to γ-NaBH₄ may occur at low temperature. At last, the pressure effects on the electronic structures of α-, β- and γ-NaBH₄ are discussed.