CO2势能面和振动激发态的理论研究

采用振动自洽场-组态相互作用(SCF-CI)方法通过实验振动光谱优化了CO₂分子的势能函数,由该势能函数计算得到的纯振动光谱数据与实验值相比,所有能级的误差均在4cm^-1以内,均方根偏差为1.50cm^-1,所预测的Π态振转光谱也与实验值很接近.     

范德华复合物Kr-C2H2的势能面和振转光谱的理论研究

采用[CCSD（T）]-F12方法和aug-cc-pVTZ基组,同时引入中心键函数（3s3p2d1f1g）构建了Kr-C₂H₂体系的高精度四维势能面.在构建势能面时考虑了分子间的振动方式及C₂H₂单体内的ν₁对称伸缩和ν₃反对称伸缩振动.将计算得到的四维势能面在Q₁方向和Q₃方向分别做积分得到C₂H₂单体分别处于振动基态和（ν₁,ν₃）=（1,1）激发态的平均势能面.计算结果表明,这2个平均势能面均存在2个等价的T型全局极小值和2个等价线性极小值.全局极小值的几何构型位于R=0.41 nm,θ=65.6°/114.4°,势阱深度为151.88 cm^-1.对径向部分采用离散变量表象法（DVR）,角度部分采用有限基组表象法（FBR）,并结合Lanczos循环算法计算了Kr-C₂H₂的振转能级和束缚态.计算结果表明,复合物在（ν₁,ν₃）=（1,1）区域的带心位移为-1.48 cm^-1,表现为红移,与实验值-1.38 cm^-1很接近;计算得到的红外跃迁频率也与实验值相吻合,说明得到的从头算势能面具有高精度.     

PdYH分子的结构与势能函数

用密度泛函理论的B3LYP方法, 对钯和钇原子采用SDD收缩价基函数, 氢原子采用6-311＋＋G**全电子基函数, 对PdY和PdYH体系的结构进行优化. 计算表明: PdY分子的几何构型为C_∞v, 其基态为X²Σ^＋态, 键长R＝0.24168 nm, 离解能为D_e＝2.8261 eV, 谐振频率ω_e＝254.0656 cm^－1, 并拟合得到Murrell-Sorbie势能函数; PdYH分子最稳态为C_s构型, 电子组态为¹A', 平衡核间距R_PdY＝0.24281 nm, R_YH＝0.19824 nm, 键角∠PdYH＝116.7157°, 离解能D_e＝5.6146 eV, 基态简正振动频率: 对称伸缩振动频率ν₁ (a')＝348.2909 cm^－1, 弯曲振动频率ν₂ (a')＝243.3382 cm^－1, 反对称伸缩振动频率ν₃ (a')＝1442.2695 cm^－1. 由微观过程的可逆性原理分析了分子的可能离解极限. 并用多体项展式理论方法分别导出基态PdY和PdYH分子的势能函数, 其等值势能面图准确地再现了PdY和PdYH分子的结构特征和离解能, 由此讨论了Pd＋Y＋H分子反应的势能面静态特征.     

氟磺酸氯分子振动光谱的从头算研究

采用从头算HF方法以6-31G^*基组研究了对ClOSO₂F分子的几何结构、振动谐性力场和红外光谱.理论力场由Pulay的标度量子力学方法进行标度,算得的振动频率与实验值比较,平均偏差为6.0cm^-1.根据振动频率的势能分布和从头算红外光谱强度值对此分子的振动基频进行了理论归属.     

α-氰基丙烯酸乙酯阴离子聚合的密度泛函理论研究

运用密度泛函理论DFT-B3LYP方法,在6-31G^*基组水平上,首次全优化计算了α-氰基丙烯酸乙酯与羟基反应势能面上的反应物、过渡态的分子几何、电子结构、能量、IR光谱和热力学性质,求得气相中反应的活化能为13.83 kJ·mol^-1,引发速率常数数量级为10¹⁰ s^-1,从热力学和动力学两方面阐明了阴离子聚合机理.通过自洽反应场(SCRF) B3LYP/6-31G^*计算,系统研究了相对介电常数分别为2.02, 2.38, 7.58和12.3的溶剂对反应物和过渡态的结构和反应机理的影响,发现溶剂效应使过渡态的活化能随极性增大而下降,并使引发反应在极性溶剂中接近于无垒反应.     

氮苄叉基苯胺及其衍生物的构象

为了探索氮苄叉基苯胺及其衍生物产生大扭角构象的根本原因,对21个分子分别在HF/6-311G^**和B3LYP/6-311G^**水平下进行了全优化和近似的势能面扫描.结果显示,分子扭曲的驱动力源于分子内的电子相互作用,片段间的核排斥作用是分子扭曲的阻力.经B3LYP/6-311G^**势能面扫描后,分别用HF,BLYP,BVWN,B3LYP和MP2法在不同的基组下对各旋转构象再作单点能运算.在简单的NBA分子中,STO-3G可以足够精确地描述分子扭曲的驱动力,但是它不能很好地描述分子内的氢键效应.     

基态H2O+的全域多体势能面

基态H₂O⁺分子离子是重要的星际反应中间体.用MRCISD/cc-pVTZ先计算H₂O⁺势能面,然后拟合成多体势能函数.全域势能面能很好地描述基态H₂O⁺的行为.与两条反应通道的实验能变和其构型翻转反应能垒比较,表明计算结果与实验值相符.对计算点完成了力场的多项式拟合,对其振动模式进行了分析     

SO2基态势能面和振转能级的理论研究

在键长-键角坐标下,精确求解SO₂的核振动方程,并通过与实验数据比较来优化势能参数,由所得势能面计算得到38个振动能级,与实验值相比,均方根误差为0.93cm^-1.计算了³⁴SO₂的部分振动能级以及³²SO₂的J=6以下的部分振动能级,所得结果均与实验值较为吻合     

ClC(O)NCS分子振动光谱的理论研究

采用密度泛函理论DFT(B3LYP)方法,以6-31G^*为基组对ClC(O)NCS的反式和顺式两种构型的几何结构、振动谐性力场和红外光谱进行了研究.B3LYP/6-31G^*的理论力场由适用于B3LYP/6-31G^*计算水平和大多数有机分子的一套固定标度因子进行标度.根据标度后的理论力场进行简正坐标分析得到的势能分布(PED)和红外光谱强度值对ClC(O)NCS分子的顺式和反式两种构型的振动基频进行了理论归属.     

SiCS分子结构及其稳定性的理论研究

采用DFT,QCISD及CCSD(T)方法对单重态、三重态SiCS的分子体系势能面进行理论计算,在QCISD/6-311G(d)水平上得到由3个过渡态连接的5个稳定构型.经动力学及热力学分析均是稳定的三重态线型分子SiCS(³1)、单重态线型分子SiCS(¹1)以及单重态的环状分子cSiCS(¹2).     

Scattering of neon atom by nitrogen molecule at thermal and subthermal energies

Collision of Ne atom with N₂ molecule in the thermal and subthermal energy regions (0.01–260 meV) has been thoroughly investigated. Centrifugally decoupled exponential distorted wave (CDEDW) method and the BSTT interaction potential have been used to calculate elastic as well as inelastic (rotational) scattering cross sections. The resonances in the very low energy region,R —Tenergy transfer mechanisms and nature of the rotational excitation cross sections near the threshold have been examined very critically. In general CDEDW method has been found to work quite well in this energy region.     

Accurate pair interaction energies for helium from supermolecular Gaussian geminal calculations

Nonrelativistic clamped-nuclei pair interaction energy for ground-state helium atoms has been computed for 12 interatomic separations ranging from 3.0 to 9.0 bohr. The calculations applied the supermolecular approach. The major part of the interaction energy was obtained using the Gaussian geminal implementation of the coupled-cluster theory with double excitations (CCD). Relatively small contributions from single, triple, and quadruple excitations were subsequently included employing the conventional orbital coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and the full configuration interaction (FCI) method. For three distances, the single-excitation contribution was taken from literature Gaussian-geminal calculations at the CCSD level. The orbital CCSD(T) and FCI calculations used very large basis sets, up to doubly augmented septuple- and sextuple-zeta size, respectively, and were followed by extrapolations to the complete basis set limits. The accuracy of the total interaction energies has been estimated to be about 3 mK or 0.03% at the minimum of the potential well. For the attractive part of the well, the relative errors remain consistently smaller than 0.03%. In the repulsive part, the accuracy is even better, except, of course, for the region where the potential goes through zero. For interatomic separations smaller than 4.0 bohr, the relative errors do not exceed 0.01%. Such uncertainties are significantly smaller than the expected values of the relativistic and diagonal Born-Oppenheimer contributions to the potential.     

Charge density distribution and electrostatic moments of N‐(4‐chloro‐3‐ trifluromethyl‐phenyl)‐2‐ethoxy‐benzamide molecule at the active site of p300 enzyme: A quantum chemical and theoretical charge density study

A Charge density analysis of CTB molecule in gas phase (Form I ) and the same present at the active site (Form II ) of p300 enzyme were performed for the wave functions obtained from the Density functional method (B3LYP) with the basis set 6‐311G**. This study has been carried out to understand the nature of conformational modification, charge redistribution and the change of electrostatic moments of the CTB molecule when present at the active site of p300. The difference of charge density distribution between both forms of CTB molecule explicitly indicates the effect of intermolecular interaction on CTB molecule in the active site. The dipole moment of CTB in the gas phase (9.6 D) has been significantly decreased (4.27 D) when it present at the active site of p300; this large variation is attributed to the charge redistribution in CTB, due to the intermolecular interaction between the CTB and the receptor p300 molecule. The electrostatic potential maps differentiate the difference of electrostatic potential between the two forms. A large electronegative region is found at the vicinity of oxygen and fluorine atoms. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

用角分布XPS法研究热处理时YBCO膜的表面组成变化及膜与衬底的相互作用

用角分布XPS法研究了MOD法制得的YBCO膜在热处理过程中膜的表面元素浓度变化以及膜与村底ZrO_2之间的原子扩散和固态化学反应。结果表明无论是薄膜(约0.1 μm)和较厚的膜(约1～1.5 μm), 在大约530～720 ℃的温度范围内加热后都发生铜表面富集和钡表面浓度偏低。在800 ℃以上加热后铜的表面浓度显著降低, 温度愈高, 降低愈甚。膜与衬底之间的化学反应也随温度升高而加剧。例如薄膜在890 ℃加热后钡向ZrO_2衬底扩散, 膜中的铜仍以+2价为主; 在950 ℃加热后衬底表面生成了富钡层, 而铜则主要以+1价的形式存在于富钡层表面。与厚膜相比, 在800 ℃以上薄膜与衬底的原子扩散和固态化学反应对于膜超导电性的损害更显著。     

Aggregation of ionic surfactants to block copolymer assemblies: a simple fluorescence spectral study

A simple and elegant method based on steady-state fluorescence spectral measurement is demonstrated to study the interaction mechanism of copolymers and ionic surfactants with a suitable selection of fluorescent probe and also its general applicability in studying other systems. Three different concentration regions have been indicated from the changes in full width at half-maximum of the emission spectra and fluorescence intensity of coumarin 153 with the molar ratio of ionic surfactant to triblock copolymer (n). At low n values, copolymer-surfactant complexes are basically copolymer-rich micelles with few surfactant molecules, and at very high n values, copolymer-rich micelles are destroyed and surfactant-rich micelles with free copolymer monomers are formed. It has been observed that, in the intermediate surfactant concentration region, the transformation of a dominantly copolymer-rich complex to a mainly surfactant-rich complex can be either gradual incorporation of surfactants into the copolymer-rich micelles with freeing of copolymer units until surfactant-rich micelles are formed (type I) or simultaneous buildup of surfactant-rich micelles together with the destruction of copolymer-rich micelles (type II). The interaction mechanism for nonionic copolymers (P123 and F127) with ionic surfactants (SDS and CTAC) is mainly type II, but at higher copolymer concentrations interaction via the type I mechanism also operates. However, it is dominantly the type I mechanism that operates for common nonionic (TX100) and ionic surfactants.     

Exploring the lower limit in hydrogen bonds: analysis of weak C-H...O and C-H...pi interactions in substituted coumarins from charge density analysis

Experimental electron densities in coumarin, 1-thiocoumarin, and 3-acetylcoumarin have been analyzed based on the X-ray diffraction data at 90 K. These compounds pack in the crystal lattice with weak C-H...O and C-H...pi interactions, and variations in charge density properties and derived local energy densities have been investigated in the regions of intermolecular interactions. Theoretical charge density calculations on crystals using the B3LYP/6-31G* method show remarkable agreement with the derived properties and energy densities from the experiment. The intermolecular interactions follow an exponential dependence of electron density and energy densities at the bond critical points. The Laplacian follows a "Morse-like" dependence on the length of the interaction line. Based on the set of criteria defined using the theory of "atoms in molecules", it has become possible to distinguish between a hydrogen bond (C-H...O) and a van der Waals interaction (C-H...pi). This has resulted in the identification of a "region of overlap" in terms of electron densities, energy densities, and mutual penetration of the hydrogen and acceptor atoms with respect to the interaction length. This approach suggests a possible tool to distinguish between the two types of interactions.     

Nanocrystallization of oligosilanes by a reprecipitation method: easy fabrication of H-aggregates of linear-chain oligosilane molecules

Nanocrystals of several oligosilanes have been fabricated easily by using a reprecipitation method. The nanocrystals reveal an intense absorption band at the UVB region (280 to 320 nm) and a fluorescence band with large Stokes shift. These photophysical properties show that the nanocrystals exhibit an excitonic interaction of the H-aggregate type.     

Efficient free energy calculation of water across lipid membranes

An efficient free energy (FE) calculation of a water molecule to go across lipid membranes is presented. Both overlapping distribution and cavity insertion Widom methods are complementarily used. The former is useful for a dense region where water molecules are found, i.e., from the interfacial to bulk water region, while the latter works well in the low density region, i.e., the hydrocarbon region. Since both methods evaluate the excess chemical potential of water, the obtained FE profile is free from the fitting problem usually arisen when a FE difference method is used. A diphytanyl phosphatidylcholine bilayer is used for our test calculations. An excellent and fast convergence of the chemical potential is obtained when each method is applied for the appropriate region. The estimated FE barrier using the Ewald method for the electrostatic interaction is approximately 7.2 kcal/mol, which is higher than that using the interaction cutoff of 20 A by about 0.9 kcal/mol.     

Kinetics of hydrogen oxidation near the lower explosion limit

Kinetics of hydrogen oxidation near the lower explosion limit in the kinetic region of chain termination has been studied. Major effects, causing deviations of the reaction kinetics from calculations by the linear theory of branched chain processes, are shown to be (1) the inhibition of the reacting mixture by the products of interaction of active centers with vacuum grease or with impurities contained in it and (2) the heterogeneous negative interaction of reaction active centers. The kinetics of hydrogen oxidation in this region has been calculated with consideration of the heterogeneous negative chain interaction. A set of parameters has been obtained that make it possible to determine by the shape of the kinetic curves the sign and the value of nonlinear interaction of chains near the lower explosion limit. It has been shown that the experimental data are in good agreement with the calculations, provided the heterogeneous negative chain interaction is taken into consideration and the inhibiting effect of impurities is eliminated. The rate of heterogeneous generation of chains on a quartz surface treated with hydrofluoric or boric acid has been determined.