铂催化甲醇氧化开始步骤的研究

用ab initio和密度泛函(DFT)方法研究甲醇在铂低指数晶面的脱氢步骤. 在经典的Bagotzky模型计算的基础上提出了三种新的吸附脱氢模型, 并通过计算证明了三种模型的可行性, 计算证实了原位波谱法检测到的甲醇在铂上脱氢的三种中间体, CHOH, CH₂OH和CH₃O. 得出了甲醇脱氢的根本原因在于形成的强Pt—H键, 且在Pt不同的晶面上, 催化性能及反应历程、中间产物都不同.     

Oxidative addition of the ethane C-C bond to Pd. An ab initio benchmark and DFT validation study

We have computed a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the ethane C-C bond to the palladium atom and have used this to evaluate the performance of 24 popular density functionals, covering LDA, GGA, meta-GGA, and hybrid density functionals, for describing this reaction. The ab initio benchmark is obtained by exploring the PES using a hierarchical series of ab initio methods [HF, MP2, CCSD, CCSD(T)] in combination with a hierarchical series of five Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account either through a relativistic effective core potential for palladium or through a full four-component all-electron approach. Our best estimate of kinetic and thermodynamic parameters is -10.8 (-11.3) kcal/mol for the formation of the reactant complex, 19.4 (17.1) kcal/mol for the activation energy relative to the separate reactants, and -4.5 (-6.8) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). Our work highlights the importance of sufficient higher angular momentum polarization functions for correctly describing metal-d-electron correlation. Best overall agreement with our ab initio benchmark is obtained by functionals from all three categories, GGA, meta-GGA, and hybrid DFT, with mean absolute errors of 1.5 to 2.5 kcal/mol and errors in activation energies ranging from -0.2 to -3.2 kcal/mol. Interestingly, the well-known BLYP functional compares very reasonably with a slight underestimation of the overall barrier by -0.9 kcal/mol. For comparison, with B3LYP we arrive at an overestimation of the overall barrier by 5.8 kcal/mol. On the other hand, B3LYP performs excellently for the central barrier (i.e., relative to the reactant complex) which it underestimates by only -0.1 kcal/mol.     

A theoretical investigation of the interaction between H,Li, Na,K, and fullerenes

We studied the interaction between H, Li, Na, and K with one and two C₆₀ molecules using unrestricted Hartree–Fock (UHF) methods. We investigated the effects of distances between the doping atoms and the C₆₀ clusters, total charges, interaction energies, stabilities, HOMO‐LUMO energy differences, charge distribution, and potential energy surfaces. The effect of each doping atom was analyzed and potential technological applications discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Photoelectron spectra of cyclopolysilanes

Summary He (I) PE spectra of cyclopentasilane and cyclohexasilane show excellent agreement with STO-3 G + ab initio calculations. The HOMO in both compounds is of (SiSi) 3 p character. First IP's appear at 9.4 and 9.6 eV respectively.

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Photoelektronenspektren von Cyclopolysilanen (Kurze Mitt.)

Zusammenfassung Die He (I) PE-Spektren der Cyclosilane Si₅H₁₀ und Si₆H₁₂ zeigen ausgezeichnete Übereinstimmung mit STO-3 G + ab initio Rechnungen. Beide Ringe besitzen HOMO's mit (SiSi) 3 p Charakter. Die ersten Ionisierungspotentiale liegen bei 9.4 bzw. 9.6 eV.

     

Ab initio and infrared spectral study of 4′-substituted phenylthiolbenzoates

The geometry of the 4′-cyano-(4′-CNPTB) and the 4′-methoxy-(4′-MePTB) phenylthiolbenzoates were obtained by ab initio calculations employing 6–31G basis set at Hartee-Fock level of theory. The results predict an extended form of the molecules and torsional angle between the phenyl rings at 90.85(6)⁰ and 90.87(3)⁰, respectively. On the basis of vibrational analysis the frequency assignment was carried out. The calculated frequencies were compared with the experimental IR spectral data in carbon tetrachloride, carbon disulfide solutions and in solid state.     

The electronic structure of small lithium clusters

Ab initio molecular orbital calculations using the STO-6G and STO6-21G basis sets have been performed for the cluster series Li _n ⁺ , Li _n , and Li _n ^– (wheren=2–7). Thirty-two optimized structures are discussed and reported, many of which (especially for the anionic structures) have not yet been considered. The calculations suggest that for all three species the optimum geometries are planar. Of the two levels of theories that were investigated, STO-6G//STO-6G and STO6-21G//STO-6G, the latter hybrid theory was found to be less reliable. In particular, for the anionic structures these calculations should provide a platform from which more sophisticated, i.e., configuration interaction, geometry optimization can be performed.     

PAN和PPN的HeI光电子能谱（PES）

给出了两个重要的大气污染化合物PAN和PPN的紫外光电子能谱（PES）。为了 指认PES谱,对两个分子实施了HF和OVGF方法的理论计算,并给出了它们各自的优 化几何构型、PES谱低电离能区的两个分离（PAN）为11.42 eV和12.07 eV;PPN为 11.08 eV和11.79 eV）被归于分子中主要体现“NO_2”基团贡献的最高占有分子轨 道（HOMO）和次最高占有分子轨道（SHOMO）电子电离作用结果。而PPN的第一电离 能11.08 eV低于PAN的11.42 eV,是由于PPN分子中增加的“CH_2”基团电子的给予 作用,这为PPN应具有较大的生物毒性提供合理的解释。     

Restricted rotation about partial C,N double bonds

The restricted rotation about the partial C,N double bond in 2-chloro-6-NR₂-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G^* level were carried out using a continuum model to take solvent effects into account. The delocalization of-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR₂ substituents (pyrrolidino > dimethylamino > morpholidino > piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR₂ substituents in the GS for the restricted rotation.     

The equilibrium C-H bond length

The equilibrium C-H bond length has been determined up to now for about 40 polyatomic molecules. These data are used to demonstrate the existence of quantitative correlations betweenr _e(C-H), isolated C-H bond stretching frequency and average distancer _g. It is also shown that ab initio calculations are often reliable to calculate the absolute value ofr _e(C-H), if an empirical correction is made. Some other correlations are also discussed. Finally, accurater _e(C-H) values are predicted for simple molecules.     

High-pressure structural trends of Group 15 elements: simple packed structures versus complex host-guest arrangements

The Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six-membered rings under ambient conditions and attain the body-centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host-guest structures emerge as intermediate pressure structures. We investigated the high-pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high-pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host-guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s-s antibonding states above the Fermi level (s-d mixing). With pressure, s-d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures.