On the vibrational spectrum of C9, C11 and C13

The harmonic frequencies and infrared intensities of C₉, C₁₁ and C₁₃ have been calculated using SCF and complete active space SCF (CASSCF) methods. The ordering of the harmonic frequencies in C₉ is predicted wrongly unless at least the π HOMO and LUMO are included in the active space. Infrared intensities depend crucially on the size of the active space. For linear odd-numbered clusters C₁₃ and larger, the computed SCF spectrum is qualitatively wrong. The recent observation of a band near 1809 cm⁻¹ in the gas phase is explained using our CASSCF results on C₁₃.     

Influence of the size of doping ion on phase stability and oxygen permeability of SrCo0.8Fe0.2O3−δ oxide

The compounds of SrCo_0.8Fe_0.2O_3−δ (SCF) doped with Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ti⁴⁺ and Zr⁴⁺ are synthesized by conventional solid-state reaction. The phase stabilities and oxygen permeabilites of these synthesized oxides are investigated. It is found that the doping Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ totally dissolve into the SCF unit cell, while SrTiO₃ and SrZrO₃ phases form when SCF is doped with Ti⁴⁺ and Zr⁴⁺, respectively. A possible mechanism of the doping behavior is proposed to interpret the structure transformation of the SCF unit cell. Phase stability increases directly with the size of the doping ion when SCF is doped with the ions in the same group. However, the influence of the size of the doping ion on the oxygen permeation behavior is negligible for the membranes doped with the ions in the same group.     

Valence-bond calculations with polarized atomic orbitals

A new method for computing polarized atomic orbitals (PAOs) is described: this method leads to very easy calculations. The space of the resulting PAOs is close to that of MC SCF MOs. Using these PAOs in the frame of a VB calculation has led to the same level of accuracy as the comparable MC SCF calculation for the dissociation energies and the lowest electronic transition energies of H₂, H₃ and N₂.     

Effect of dopant valence on the oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M -Ni,Al and Zr） mixed-conducting oxides

The effect of dopant valence on oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M = Ni, Al and Zr） mixed-conducting oxides were investigated in detail by O2-TPD and oxygen permeation measurement. The SrCo0.4Fe0.5M0.1O3-δ for M = Fe, Ni, Al and Zr were denoted as SCF, SCFN, SCFA and SCFZ, respectively. O2-TPD analysis revealed that the amount of α oxygen desorption decreased with increasing the valance of doped metal elements （SCFN 〉 SCFA SCF 〉 SCFZ）. The oxygen permeation flux at the temperature ≈igher than 1148 K decreased in the order of SCFN 〉 SCF 〉 SCFZ 〉 SCFA. Single activation for oxygen permeation was observed for SCFZ oxide and the activation energies of SCF and SCFA change at around 1073 K, while the change temoerature of SCFN was about 1173 K.     

Non-empirical calculations on diatomic transition metals. I. An investigation of various orbital contraction schemes of gaussian basis sets on the SCF level for Zn2

Ab initio SCF LCAO MO calculations with various contracted primitive gaussian basis sets were performed using Zn₂ as an example. When improving the basis set, polarization functions are shown to be more important for a proper reproduction of the repulsive potential curve, than a complete relaxation of the orbital contraction. This is considered to be true for all diatomics although for Zn₂ at larger internuclear distances no varr der Waals minimum is obtained on the SCF level.     

AB initio study of the regular polyhedral molecules N4, P4, As4, N8, P8 and As8

Ab initio pseudopotential SCF calculations were performed on tetrahedral X₄ molecules using double-zeta basis sets with and without d functions. The inclusion of d orbitals shortens the bond lengths, stabilizes the X₄ structures and intensifies the electron density inside the tetrahedron. The cubic X₈ molecules, calculated without d AOs, are not predicted to be more stable than 2X₄. Repulsions between parallel bonds in X₈ may compensate the lack of ring strain.     

Tridimensional structure of the zinc cyanide ion [Zn27(CN)55] determined by quantum mechanical calculations (QMC) as a complementary method to force field (FF)

The aim of this work was to determine the lowest energy conformation of the [Zn₂₇(CN)₅₅]⁻ ion using ab initio SCF techniques. The theory on atoms in molecules was used to characterize both the normal bonds and the intermolecular interactions responsible for the helical structure type.     

Many-body perturbation theory and polarization propagator studies of the structure, energetics and excitation spectrum of CO3

Geometry optimization has been performed on CO₃ in the SCF approximation and in the second-, third-, and fourth-order MBPT approximations limited to single and double substitutions using a double-zeta plus polarization basis set. The energetics of the formation and decomposition of CO₃ from the reactions CO₂ + O(¹D) → CO₃ and CO₃ + CO → 2CO₂, respectively, have been calculated in several approximations including full fourth-order MBPT. In addition first-order polarization propagator calculations have been performed to identify the low-lying excited states.     

An SCF potential energy and dipole surface for rubidium cyanide (RbCN)

Ab initio SCF computations of the potential energy and dipole moment surface of RbCN are reported. The surfaces are represented in an analytic form suitable for the computation of the rovibrational spectrum. The molecule is predicted to be triangular with distances, r(C---N) = 2.186 a₀, r(C---Rb) = 5.811 a₀ and r(N---Rb) = 5.082 a₀.     

Ab initio MO calculation of force constants and dipole derivatives for the formamide dimer. An estimation of hydrogen-bond force constants

Ab initio SCF MO calculations (with the 4-31G basis set) have been carried out to determine the equilibrium geometry, vibrational frequencies, dipole-moment derivatives, and force constants for intermolecular modes of the formamide dimer and its d₄ and d₆ derivatives. The results are correlated with monomer calculations and experimental data for crystalline formamide.     

EDTA-柠檬酸法合成的SrCo0.8Fe0.2O3-δ钙钛矿的结构及制氧性能研究

采用EDTA-柠檬酸联合络合法合成了钙钛矿型金属氧化物SrCo_0.8Fe_0.2O_3-δ(SCF182)粉体。通过XRD和ESEM研究了前驱体溶液不同的pH值对合成的SCF182粉体的晶体结构和微观形貌的影响。并采用固定床实验研究前驱体溶液pH值对SCF182的氧吸附/脱附性能的影响。结果表明,pH值对SCF182晶胞结构和参数影响不大,但影响SCF182的晶粒粒径和微观形貌,当pH值为8的弱碱性条件下时,能够合成蓬松多孔网状纳米结构的钙钛矿粉体。固定床实验显示,前驱体溶液的pH值影响合成的粉体SCF182的氧吸附速率;且SCF182的氧脱附性能随pH值的增大先升高后降低,pH值为8时氧脱附量达到峰值为42.2 mg/g。     

Effect of small cations on the hydrogen bond between an N-aromatic heterocycle and amine

The influence of an Li⁺ ion on the structure and bonding of the H-bond interaction of an N-aromatic heterocycle and a singly bonded N-amine is studied by ab initio SCF calculations with imidazole (Imh) and NH₃ serving as models of the two families. Full optimization of structures have been carried out for DZ, DZP and TZP basis sets. The computed H-bond energy for Imh/ NH₃ of −6.4 kcal/mol is in close agreement with a recent experiment. An appreciable three-body interaction of −3.8 kcal/mol is found for the complex Imh/NH₃/Li⁺.     

CAS SCF and contracted CI calculations on the HO3 radical

CAS SCF and CCI calculations have been performed in order to establish the existence or non-existence of the HO₃ radical. The potential surface for the dissociation reaction, HO₃ → O₂(³Σ) + OH, along one chosen coordinate has been calculated. The calculations show that although the wavefunctions describing the short-distance and long-distance states are of different character, the energies are the same and the curve connecting the states is very flat. There is probably no barrier towards dissociation of the radical. However, the existence of HO₃ can still not be excluded.     

INDOStudiesonElectronicStructuresof（C＿8H＿8）Ln（2，4－C＿4H＿11）（THF）（Ln＝Nd，Sm，Er）

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Relative stabilities of the asymmetric OPOP, symmetric OPPO and cyclic conformations of P2O2

Various P₂O₂ planar isomers are investigated by molecular orbital calculations. Cyclic (¹A_g) is predicted to be more stable than OPOP (³A″-cis) and OPPO (¹A_g-trans) by 5.6 and 23.1 kcal/mol, respectively. The dimerization energy of 2PO→cyclic OPOP lies around 55 kcal/mol; the asymmetrical conformations OPOP and symmetrical OPPO are also bound. The computed vibrational frequencies and corresponding absorption intensities (derived at the SCF level) should help future experimental characterizations of these P₂O₂ isomers.     

Ab initio molecular orbital calculations of nuclear spin-spin coupling constants in PH2, PH3, PH4 and P2H4

Ab initio molecular orbital calculations of nuclear spin-spin coupling constants in PH⁻₂, PH₃, PH⁺₄ and P₂H₄ have been carried out employing SCF perturbation theory. Basis set dependence of all the four contributing terms has been studied in order to find the criterion for the selection of basis sets to be employed for computing this property. The dependence of the coupling constants of PH⁻₂ on its geometry has also been found. This study also discusses the requirement for satisfactory computation of couplings in cases where none of the coupling nuclei is a proton. It is found that bond-centred functions along with at least double zeta basis sets reproduce coupling constants quite satisfactorily. In all the cases studied, uncontracted core basis functions yield couplings which are in better agreement with experimental couplings than those obtained with contracted core functions.     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

The sign of the spin-orbit coupling constant in (t2) t2 states of mx4 ions

It is shown that the sign of the spin-orbit coupling constant in ²T₂ states of MX⁺₄ molecular ions (M = C, Si, Ge; X = F, Cl, Br, I) arising from the (t₂)⁵ electron configuration can be positive, negative or even zero. Predominantly, the sign depends on the orientation of the p-orbitals on the four halogen atoms with respect to the M-X bonds. Experimentally observed splittings show that it is incorrect to describe the two highest t2 valence orbitals of MX₄ as pure pπ non-bonding and pure pσ bonding, since both exhibit pσ/pπ mixing. This is confirmed by semi-empirical SCF MNDO molecular-orbital calculations.     

Valence and core ionization energies for SiH4, H3SiCl and H3CCl from SCF and PNO-CEPA calculations

Valence and core ionization energies for the molecules SiH₄, H₃SiCl and H₃CCl have been obtained from RHF-SCF and PNO-CEPA wavefunctions. The calculated vertical ionization energies IE_n^v(n = 1, 2, 3) agree within about 0.2 eV with the PE spectroscopically determined values for SiH₄, H₃SiCl and H₃CCl. The increase in IE₁^v for H₃SiCl relative to H₃CCl, which has been previously ascribed to a different d-orbital participation in the two molecules, is already reproduced by calculations with (s, p) basis sets. The ΔSCF method has been used to predict several core ionization energies. In addition, relative intensities calculated for the ionizations into the ²A₁ states of SiH₄⁶ are compared with available experimental data, and some spectroscopic constants for SiH₄ and its ionic states are predicted.