超价化合物M_(n+1)F_n(n=1,2;M=Na,K)体系的非线性光学性质的理论研究

采用UMP2/6-311+G(3df)方法研究了一系列化合物M_(n+1)F_n(n=1,2;M=Na,K)体系的几何构型及非线性光学性质(NLO).结果表明:这些体系均为超价化合物,均拥有较大的第一超极化率(β_0).尤其是Na_3F_2体系中结构2c的β_0值为29.16×10~(-49)C~3·m~3·J~(-2),是已知超价化合物Li_3F_2的2c结构的β_0值2.22×10~(-49)C~3·m~3·J~(-2)的13.1倍.     

Ab initio investigation of water clusters (H2O)n (n = 2–34)

Various properties of typical structures of water clusters in the n = 2–34 size regime with the change of cluster size have been systematically explored. Full optimizations are carried out for the structures presented in this article at the Hartree–Fock (HF) level using the 6‐31G(d) basis set by taking into account the positions of all atoms within the cluster. The influence of the HF level on the results has been reflected by the comparison between the binding energies of (H₂O)_n (n = 2–6, 8, 11, 13, 20) calculated at the HF level and those obtained from high‐level ab initio calculations at the second‐order Møller–Plesset (MP2) perturbation theory and the coupled cluster method including singles and doubles with perturbative triples (CCSD(T)) levels. HF is inaccurate when compared with MP2 and CCSD(T), but it is more practical and allows us to study larger systems. The computed properties characterizing water clusters (H₂O)_n (n = 2–34) include optimal structures, structural parameters, binding energies, hydrogen bonds, charge distributions, dipole moments, and so on. When the cluster size increases, trends of the above various properties have been presented to provide important reference for understanding and describing the nature of the hydrogen bond. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Ab initio calculations on XFnq (X = I,Xe, Cs,and Ba; n=1, 2, 4, and 6; q=−1, 0, +1, and +2) molecules

Ab initio calculations employing relativistic effective core potentials were carried out to investigate the electronic structure of xenon fluoride molecules. The chemical bonds and geometrical stability of some isoelectronic ions, which have the central atom replaced by iodine, cesium, and barium ions, were also investigated. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 238–245, 2001     

Structure and bonding in cyclic isomers of BAl2Hnm (n=3-6, m=-2 to +1): preference for planar tetracoordination, pyramidal tricoordination, and divalency

The structure and energetics of cyclic BAl2Hnm (n=3-6, m=-2 to +1), calculated at the B3LYP/6-311+G** and QCISD(T)/6-311++G** levels, are compared with their corresponding homocyclic boron and aluminium analogues. Structures in which the boron and aluminium atoms have coordination numbers of up to six are found to be minima. There is a parallel between structure and bonding in isomers of BAl2H(3)2- and BSi2H3. The number of structures that contain hydrogens out of the BAl2 ring plane is found to increase from BAl2H3(2-) to BAl2H6+. Double bridging at one bond is common in BAl2H5 and BAl2H6+. Similarly, species with lone pairs on the divalent boron and aluminium atoms are found to be minima on the potential energy surface of BAl2H(3)2-. BAl2H4- (2 b) is the first example of a structure with planar tetracoordinate boron and aluminium atoms in the same structure. Bridging hydrogen atoms on the B--Al bond prefer not to be in the BAl2 plane so that the pi MO is stabilised by pi-sigma mixing. This stabilisation increases with increasing number of bridging hydrogen atoms. The order of stability of the individual structures is decided by optimising the preference for lower coordination at aluminium, a higher coordination at boron and more bridging hydrogen atoms between B--Al bonds. The relative stabilisation energy (RSE) for the minimum energy structures of BAl2Hnm that contain pi-delocalisation are compared with the corresponding homocyclic aluminium and boron analogues.     

Ab Initio Theoretical Investigation on the Geometrical and Electronic Structures of AlAun-/0 (n = 2-4) Clusters

A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of AlAu n 0/-(n=2-4) clusters has been performed in this work. AlAu n-anions prove to possess ground states of the V-shaped C2v AlAu2 - , umbrella-shaped C3v AlAu3- , and perfect tetrahedral T d AlAu4- , while their neutrals favor the V-shaped C2v AlAu2 , perfect planar triangular D3h AlAu3 , and severely distorted C s AlAu4 , respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C s AlAu4 . Molecular orbitals (MOs) analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in Al-Au bonds, which is smaller than the BAu n0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of Al-Au bonds between 100-400 cm -1 have been calculated to facilitate future experimental characterization of these clusters.     

Electronic structure and stability of BP clusters: theoretical calculations for (BP)n (n = 2–4)

The geometry, electronic configurations, harmonic vibrational frequencies, and stability of the structural isomers of boron phosphide clusters have been investigated using density functional theory (DFT). CCSD(T) calculations show that the lowest‐energy structures are cyclic (IIt, IVs) with D_nh symmetry for dimers and trimers. The caged structure for B₄P₄ lie higher in energy than the monocyclic structure with D_2d symmetry (VIs). The B–P bond dominates the structures for many isomers, so that one preferred dissociation channel is loss of the BP monomer. The hybridization and chemical bonding in the different structures are also discussed. Comparisons with boron nitride clusters, the ground state structures of B_nP_n (n = 2, 3) clusters are analogous to those of their corresponding B_nN_n (n = 2, 3) counterparts. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Ab initio molecular dynamics studies of ionic dissolution and precipitation of sodium chloride and silver chloride in water clusters, NaCl(H2O)n and AgCl(H2O)n, n = 6, 10, and 14

An ab initio molecular dynamics method was used to compare the ionic dissolution of soluble sodium chloride (NaCl) in water clusters with the highly insoluble silver chloride (AgCl). The investigations focused on the solvation structures, dynamics, and energetics of the contact ion pair (CIP) and of the solvent-separated ion pair (SSIP) in NaCl(H(2)O)(n) and AgCl(H(2)O)(n) with cluster sizes of n = 6, 10 and 14. We found that the minimum cluster size required to stabilize the SSIP configuration in NaCl(H(2)O)(n) is temperature-dependent. For n = 6, both configurations are present as two distinct local minima on the free-energy profile at 100 K, whereas SSIP is unstable at 300 K. Both configurations, separated by a low barrier (<10 kJ mol(-1)), are identifiable on the free energy profiles of NaCl(H(2)O)(n) for n = 10 and 14 at 300 K, with the Na(+)/Cl(-) pairs being internally solvated in the water cluster and the SSIP configuration being slightly higher in energy (<5 kJ mol(-1)). In agreement with the low bulk solubility of AgCl, no SSIP minimum is observed on the free-energy profiles of finite AgCl(H(2)O)(n) clusters. The AgCl interaction is more covalent in nature, and is less affected by the water solvent. Unlike NaCl, AgCl is mainly solvated on the surface in finite water clusters, and ionic dissolution requires a significant reorganization of the solvent structure.     

Theoretical dynamic studies on the reactions of CH3C(O)CH3-nCl(n) (n = 0-3) with the chlorine atom

The theoretical investigations were performed on the reaction mechanisms for the title reactions CH(3)C(O)CH(3) + Cl --> products (R1), CH(3)C(O)CH(2)Cl + Cl --> products (R2), CH(3)C(O)CHCl(2) + Cl --> products (R3), and CH(3)C(O)CCl(3) + Cl --> products (R4) by ab initio direct dynamics approach. Two different reaction channels have been found: abstract of the H atom from methyl (--CH(3)) group or chloromethyl (--CH(3-n)Cl(n)) group of chloroacetone and addition of a Cl atom to the carbon atom of the carbonyl group of chloroacetone followed by methyl or chloromethyl eliminations. Because of the higher potential energy barrier, the contribution of addition-elimination reaction pathway to the total rate constants is very small and thus this pathway is insignificant in atmospheric conditions. The rate constants for the H-abstraction reaction channels are evaluated by using canonical variational transition state theory incorporating with the small-curvature tunneling correction. Theoretical overall rate constants are in good agreement with the available experimental values and decrease in the order of k(1) > k(2) > k(3) > k(4). The results indicate that for halogenated acetones the substitution of halogen atom (F or Cl) leads to the decrease in the C--H bond reactivity and more decrease of reactivity is caused by F-substitution.     

Electronic Structures of LixV2O5 (x=0.5 and 1): A Theoretical Study

The electronic properties of α‐Li_xV₂O₅ (x=0.5 and 1) are investigated using first principle calculations based on density functional theory with local density approximation. Different intercalation sites for Li in the V₂O₅ lattices are considered, showing different influences on the electronic structures of Li_xV₂O₅. The lowest total energy is found when Li is only intercalated along the c axis between two bridging oxygen ions of sequential V₂O₅ layers. The intercalation of Li into V₂O₅ does not change the electron transition property of V₂O₅, which is an indirect band gap semiconductor, but leads to a reduction of vanadium ions and an increase of the Fermi level of Li_xV₂O₅ arising from the electron transfer from the Li 2 s orbital to the initially empty conduction band of the V₂O₅ host.     

2, 4-二羟基苯甲醛缩硫脲及其配合物构象及生理活性的理论研究

缩氨基硫脲类衍生物及其金属配合物是20世纪70年代初期人们认为具有潜在生物活性的化合物,具有抗菌、抗病毒及抗癌等生物活性犤1～4犦。我们曾对2,4-二羟基苯甲醛缩硫脲及其与Cu?、Zn?、Ni?的配合物的合成和生物活性进行过研究犤5犦。但由合成方法和物理表征仅能知道其一维连接顺序,而它们的构象及生理活性的理论研究尚未见报道。现代药物分子设计理论认为,药物分子(底物)的活性取决于与生物大分子(受体)活性中心作用时相匹配的活性构象。因此,探讨药物分子的构效关系(QSAR)对药物分子的生理活性研究至关重要。本文利用Gaussian98W在HF…     

线性阳离子NC2nN+(n=1-5)的结构和电子光谱的理论研究

运用RCCSD(T)的研究了线性阳离子NC2nN+(n=1-5)的基态平衡几何构型.结果表明,这些物种都具有单-叁键交替的结构.采用CASPT2方法,得到了体系的偶极允许跃迁的垂直激发能分别是2.26 eV,2.09 eV,1.91 eV,1.72 eV和1.56 eV,与可利用的实验值(2.15 eV,2.08 eV...     

DFT and ab initio direct dynamics studies on the hydrogen abstraction reactions of chlorine atoms with CH(4-n)F(n) (n = 1-3)

A direct dynamics study is carried out for the hydrogen abstraction reactions Cl + CH(4-n)F(n) (n = 1-3) in the temperature range of 200-1,000 K. The minimum energy paths (MEPs) of these reactions are calculated at the BH&H-LYP/6-311G(d,p) level, and the energies along the MEPs are further refined at the QCISD(T)/6-311+G(2df,2p) and QCISD(T)/6-311+G(d,p) (single-point) level. The rate constants obtained by using the improved canonical variational transition state theory incorporating small-curvature tunneling correction (ICVT/SCT) are in good agreement with the available experimental results. It is shown that the vibrational adiabatic potential energy curves for these reactions have two barriers, a situation similar to the analogous reactions CH(3)X+Cl (X=Cl, Br). The theoretical results show that for the title reactions the variational effect should not be neglected over the whole considered temperature range, while the small-curvature tunneling effect is only important in the lower temperature range. The effects of fluorine substitution on the rate of this kind of reactions are also examined.     

Theoretical study of aromaticity in small hydrogen and metal cation clusters X (X=H,Li, Na,K, and Cu)

Five cation clusters X (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D_3h) and linear structure (D_∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D_3h) is stable. The related neutral clusters X₃Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H₃Cl species, there is no a stable structure to be found. For other four X₃Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C_2v‐1) [see Fig. 1 (d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

AlCn及AlC+n(n=1-4)原子簇的理论研究

用ab initio能量解析梯度法，在UHF（RHF）／3－21G水平上优化得到AlCn，AlCn+（n＝1～3）的四十三个构型，在RHF（UHF）／3－21G水平上优化得到AlC4，AlC4+的二十六个构型，CISD能量．从能量角度所研究的AlCn，AlCn+（n=1～4）构型中，最稳定的构型均是线性构型，且Al全都在端点上，同文献报导的理论和实验结果相一致．此外，还研究了原子簇的离子化能，原子平均结合能以及原子簇的碎片化通道和碎片化能，并计算了上述最稳定构型的谐振动光谱常数．     

Theoretical study on the insertion reactions of Ti+(2F) with HF,HCl, H2O,H2S,NH3, PH3, CH4, and SiH4

The insertion reactions of the titanium atom cation Ti⁺(²F) into HF, HCl, H₂O, H₂S, NH₃, PH₃, CH₄, and SiH₄ have been studied by ab initio molecular orbital theory. All these reactions involve the initial formation of an intermediate complex followed by a hydrogen migration process via a transition state to inserting product. The Ti⁺(²F) insertion into eight compounds' reactions show that the reaction with hydride of the right‐hand group is more exothermic than that of the left‐hand group and has a lower overall barrier, and that the reaction with the second‐row hydride has a lower overall barrier and is less exothermic than with the first‐row hydride. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 47–54, 1999     

Theoretical study of ScCO2+

The structure, binding energy, and vibrational frequencies have been determined for ScCO₂⁺. The inserted OSc⁺CO structure in the ¹A′ state is the most stable isomer and lies 43.2 kcal/mol below the ground-state Sc⁺+ CO₂ asymptote. The linear η¹-O Sc⁺(SINGLE BOND)OCO ³Δ state is bound by a charge-quadrupole interaction and has a binding energy of 13.9 kcal/mol. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 523–528, 1997     

Direct ab initio dynamics study on the rate constants and kinetic isotope effect for the reactions of H atoms with GeDn(CH3)4-n (n = 1-4)

Direct ab initio dynamic calculations are performed on the reactions of atomic hydrogen with GeD(n)(CH(3))(4-n) (n = 1-4) over the temperature range 200-2000 K at the PMP4SDTQ/6-311 +G(3df,2p)//MP2/6-31 +G(d) (for n = 2-4) and G2//MP2/6-31 +G(d) (for n = 1) levels. The corresponding k(H)/k(D) ratios are then calculated in order to determine the kinetic isotope effect for the four reactions. For the simplest GeD(4) +H reaction, the only one that has available experimental data, the calculated canonical variational transition state theory incorporates small-curvature tunneling correction (CVT/SCT) thermal rate constants, and the k(H)/k(D) values are in good agreement with the experimental values within the experimental temperature range 293-550 K. For the four GeD(n)(CH(3))(4-4) (n = 1-4) reactions, the variational effect is small over the whole temperature range, whereas the small-curvature effect is important in the lower temperature range. Finally, the overall rate constants are fitted to the three-parameter expression over the whole temperature range 200-2000 K as 5.8 x 10(8)T(1.68)exp(-929/T), 1.7 x 10(8)T(1.80)exp(-691/T), 2.58 x 10(8)T(1.71)exp(-706/T), and 1.0 x 10(7)T(2.08)exp(-544/T) cm(3) mol(-1) s(-1) for the n = 4, 3, 2, and 1 reactions. Our work may represent the first theoretical study of the kinetic isotope effect for the H-attack on the G-H bonding.     

An Ab Initio Study of C2H2.H2, C2H2.N2, and C2H2.Ar Complexes

Ab initio calculations at the post Hartree–Fock level were performed on complexes of acetylene with hydrogen, nitrogen, and argon. Total energies, optimum geometries, and binding energies were calculated, using the 6-311G** and the 6-31+G(2df,2pd) basis sets. Calculations showed the complexes to be more stable than the separate entities, with the exception of the acetylene–hydrogen complex.