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Complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with contracted ANO-RCC basis set were performed for low-lying electronic states of CH3SS and its cation in Cs symmetry. For the ground state X2A″ of CH3SS, the calculated S-S stretching mode is in good agreement with experimental reports. The electron transitions of CH3SS+, X1A′ 11A″, X1A′ 21A′, and X1A′ 21A″, are predicted at 1.055, 3.247, and 3.841 eV. Moreover, the calculated adiabatic and vertical ionization potential and adiabatic affinity are in reasonable agreement with the experimental data. The CASSCF/CASPT2 potential energy curves (PECs) were calculated for S2-loss dissociation from the X2A″, 12A′, and 22A″ states. The electronic states of the CH3 radical and S2 molecule as the dissociation products were carefully determined by checking energies and geometries of the asymptote products. The S2-loss PEC for CH3SS indicate that S2-loss dissociation occurs from the X2A″ state leading to CH3 (12A″) + S2 (X3Σ), the 12A′ and 22A″ leading to CH3 (12A″) + S2 (1Δg). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012.

The reaction of C2(A3Πu) with CH4 has been investigated over a wide temperature range 200–3,000 K by direct ab initio dynamics method at the BMC-CCSD//BB1K/6-311+G(2d,2p) level of theory. The optimized geometries and frequencies of the stationary points are calculated at the BB1K/6-311+G(2d,2p) level, and then the energy profiles of the reactions are refined using the BMC-CCSD method. The activation barrier height for H-abstraction reaction was calculated to be 4.44 kcal/mol in temperature range (337–605 K), and the electron transfer behavior was also analyzed by quasi-restricted molecular orbital method in detail. The canonical variational transition-state theory (CVT) with the small curvature tunneling (SCT) correction method is used to calculate the rate constants over a wide temperature range 200–3,000 K. The theoretical results shows that variational effect is to some extent large in lower temperature range, and small curvature and tunneling effect play important roles to the H-atom abstraction only at lower temperatures. The CVT/SCT rate constants are in good agreement with the available experimental results. Our theoretical study is expected to provide a direct insight into the reaction mechanism and may be useful for estimating the kinetics of the title reaction over a wide temperature range where no experimental data are available so far. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

In the short zigzag-edged aza-Mobius graphene ribbon [2,7], a Li atom monosubstitutes the end H atom from the knot subring (1) to the subring (7), respectively, seven structures of short monolithiated aza-Mobius graphene ribbon isomers [MoLi (1), MoLi (2), MoLi (3), MoLi (4), MoLi (5), MoLi (6), and MoLi (7)] with all the real frequencies are obtained at the B3LYP/6-31G (d) level. The results of the static first hyperpolarizabilities (β0) show that lithiation effect on β0 is obvious. The β0 value of MoLi (4) (1019 a.u.) is about 4 times of 250 a.u. of the aza-Mobius graphene ribbon. For the lithiated Mobius isomers, the lithium-orientation effect is exhibited. The lithiated subring is or near the knot subring, the isomers [MoLi (1), MoLi (2), and MoLi (7)] have small β0 values, while that is far away from the knot subring, the isomers [MoLi (4) and MoLi (5)] have large β0 values. For the MoM (1) (M = Li, Na, and K), the alkali atomic number dependence for the static hyperpolarizability (α0) and β0 is found that both the α0 and β0 value increase with increasing the alkali atomic number in the orders of 275.27 (M = Li) < 279.75 (M = Na) < 284.77 a.u. and 352 (M = Li) < 590 (M = Na) < 706 a.u. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

In this article, a group-theoretical discussion is presented to show that both the spin projection operators proposed by Lowdin and the characteristic operators which have been proposed by Tang and Guo to perform unilarily invariant decomposition of Hermitian operators are in essence equivalent, and they act as two distinct realizations of idempotents of SU(2) to give two different, permutation and unitary, symmetries, respectively. By means of either the spin projection operators or the characteristic operators, the explicit form of the Sanibel coefficients can be obtained directly.

This paper works out the double tensors of the chain Q ⊂ G, where Q and G represent a point group and its subgroup of lower symmetry, respectively. By using techniques of the fractional parentage coefficient (FPC) and of the Wigner-Eckart theorem, the matrices of electrostatic interaction in terms of molecular parameters are performed. Similarly, the matrices of spin-orbital interaction are accomplished as well.

The coordination chemistry of polydentate chelating ligands that contain mixed pyridinephenol donor sets has been a sought-after target of study and is a possible extension to the chemistry of polypyridines. In this article, seven compounds, which are the four-coordinate boron complexes containing the mixed phenol-pyridyl group, have been studied by theoretical calculation. They can function as charge transport materials and emitters, with high efficiency and stability. To reveal the relationship between the structures and properties of these bifunctional or multifunctional electroluminescent materials, the ground and excited state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials (IPs) and electron affinities (EAs) were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The lowest excitation energies, and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory method. As a result of these calculations, the values of HOMO, LUMO, energy gaps, IPs, EAs, and the balance between the hole- and electron-transfer are greatly improved with the substitution of carbazole in compound 6. The calculated emission spectra of the seven studied molecules can almost cover the full UV-vis range (from 447.4 to 649.3 nm). Also, the Stokes shifts are unexpectedly large, ranging from 139.4 to 335.1 nm. This will result in the relatively long fluorescence lifetimes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

The reaction of N (2D) radical with NO2 molecule has been studied theoretically using density functional theory and ab initio quantum chemistry method. Singlet electronic state [N2O2] potential energy surfaces (PES) are calculated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311+G(d) + ZPE and G3B3 levels of theory. All the involved transition states for generation of (2NO) and (O2 + N2) lie much lower than the reactants. Thus, the novel reaction N + NO2 can proceed effectively even at low temperatures and it is expected to play a role in both combustion and interstellar processes. On the basis of the analysis of the kinetics of all pathways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

The structures, spectroscopies, and stabilities of the doublet Si2NO radical are explored at the density functional theory (DFT) and ab initio levels. Seventeen isomers are located, connected by 26 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, three low-lying isomers are predicted, that is, one bent species SiNSiO 3 (5.1 kcal/mol) containing the important SiN triple bonding and two four-membered ring isomers including cyclic cSiNSiO 1 (0.0) with SiSi cross-bonding with C2v symmetry and puckered cSiNSiO 1′ (11.9) with divalent carbene character. Three low-lying isomers 1, 1′, and 3 have reasonable kinetic stabilities and might be observable either experimentally or astrophysically. The possible formation strategies of 1, 1′, and 3 in laboratory and in space are discussed in detail. The calculated vibrational frequencies and possible formation processes of 3 are consistent with recent experimental observations. In light of the fact that no cyclic nitrogen-containing species have been detected in space, two cyclic isomers 1 and 1′ could be promising candidates. Furthermore, the bonding nature of three isomers 1, 1′, and 3 is analyzed. The calculated results are also compared with those of the analogue C2NO radical. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

The structural properties of neutral and ionic AlnO2 (n = 1–10) clusters have been systematically investigated using the density functional method B3LYP with a standard 6-311+G(d) basis set. The calculated results show that in the AlnO, AlnO2, and AlnO (n ≥ 3) clusters, O atoms tend to penetrate into the aluminum clusters with some Al atoms moving outward. The binding energies and natural charges populations indicate that the oxygen-etching is generally stronger in the order Al Aln > Al for n ≥ 3. To further understand the mechanism of interaction between Al and O2, the adsorption of O2 on the Al(111) surface was studied using the density functional theory with plane wave pseudopotential method. The calculated results are consistent with the experimental observation that the O2 molecule would dissociate on the Al(111) surface and be adsorbed in adjacent hollow sites, forming a local structure of Al3O–Al3O. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Using four basis bets, (6-311G(d,p), 6-31+G(d,p), 6-31++G(2d,2p), and 6-311++G(3df,3pd), the optimized structures with all real frequencies were obtained at the MP2 level for the dimers CH2OHF, CH2OH2O, CH2ONH3, and CH2OCH4. The structures of CH2OHF, CH2OH2O, and CH2ONH3 are cycle-shaped, which result from the larger bend of σ-type hydrogen bonds. The bend of σ-type H-bond O…HY (YF, O, N) is illustrated and interpreted by an attractive interaction of a chemically intuitive π-type hydrogen bond. The π-type hydrogen bond is the interaction between one of the H atoms of CH2O and lone pair(s) on the F atom in HF, the O atom in H2O, or the N atom in NH3. In contrast with the above three dimers, for CH2OCH4, because there is not a π-type hydrogen bond to bend its linear hydrogen bond, the structure of CH2OCH4 is noncyclic shaped. The interaction energy of hydrogen bonds and the π-type H-bond are calculated and discussed at the CCSD (T)/6-311++G(3df,3pd) level. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

The possible geometrical structures and relative stability of silicon-sulfur clusters (SiS2) (n = 1-6) are explored by means of density functional theory (DFT) quantum chemical calculations. We also compare DET with second-order Moller-Plesset (MP2) and Hartree-Fock (HF) methods. The effects of polarization functions, diffuse functions, and electron correlation are included in MP2 and B3LYP quantum chemical calculations, and B3LYP is effective in larger cluster structure optimization, so we can conclude that the DFT approach is useful in establishing trends. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS2)(n)(-) are analyzed by B3LYP. As a result, the regularity of the (SiS2)(n)(-) cluster growing is obtained, and the calculation may predict the formation mechanism of the (SiS2)(n)(-) cluster. (C) 2001 John Wiley & Sons, Inc.

The heterofullerenes C59N and C69N and their dimers are examined by the intermediate neglect of differential overlap (INDO/1 and INDO/S) models. The results confirm the stability of the (C59N)2 and (C69)2 (C2h) isomers with a 6–6 closure fusion link between the two monomers. The nearest neighbor C of nitrogen, at the hexagon–hexagon fusion in C59N and in C69N where the N replaces one C in the pentagon of the fullerene has the largest electronic spin density, and this is where the two radicals of C59N or C69N link to form dimers. Also the dimers readily dissociate to free radical monomers to react regioselectively with other reagents. The electronic spectra of the radicals are similar to those of the dimers, which suggest essentially identical electronic structures. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 422–436, 2000

Intermediate neglect of differential overlap (INDO) calculations were used to study two structures of C{sub 60}NH{sub 2}{sup +}: one of C{sub 2{sub nu}} geometry with a bridging NH{sub 2}{sup +} across the bond between two fused six-membered rings in C{sub 60} and the other of C{sub s} geometry with a bridging NH{sub 2}{sup +} across the bond between a five- and a six-membered ring. We calculated the most stable isomer of C{sub 60}NH{sub 2}{sup +} to be of C{sub 2{sub nu}} symmetry. It was found that the C{sub 2v} isomer has a protonated aziridine structure with a bridging C-C bond length of 0.1520 nm. The electronic spectra of both isomers of C{sub 60}NH{sub 2}{sup +} were calculated. Comparisons were made with the isoelectronic molecules C{sub 60}O and C{sub 60}CH{sub 2}, cases in which the calculated electronic spectra for the most stable isomers C{sub 60}O (C{sub 2v}) and C{sub 60}CH{sub 2} (C{sub 2{nu}}) are in good agreement with recent experimental results. 22 refs., 5 figs., 10 tabs.

The equilibrium geometry and UV-visible spectra of C{sub 70} were examined using semiempirical INDO/2 and INDO/CI methods. The results obtained are in good accord with experimental results. On the basis of correct electronic spectra, calculations of the nonlinear third-order optical susceptibility ({gamma}{sub ijkl}) of C{sub 70} were performed using the INDO/SDCI method combined with a sum-over-states expression. The calculated value for ({gamma})({minus}2{omega}; {omega}, {omega}, 0) is 0.882 {times} 10{sup {minus}33} esu ({omega} = 1.91 {mu}m), which is in good agreement with observation. 17 refs., 2 figs., 4 tabs.

Calculations of the nonlinear second-order optical susceptibilities (βijk) for disubstituted conjugated organic molecules are reported. The calculations are performed using the semiempirical INDO/CI method combined with a sum-over-states expression for βijk. The calculated results show that the second-order static susceptibility (β0) varies as the 2.6 power of the length of the conjugated π-electron system. Furthermore, it is found that the amount of substituent charge transfer from ground state to first excited state decreases with inccreasing chain length. A limiting value of β0 with the length of the conjugated system is discussed.

The groups with local symmetries are employed to explore the intrinsic symmetries of various kinds of cycloadditions to become apparent ones. For the electrocyclic reactions, the concept of local symmetry can still be applied equivalently, but no new result can be achieved. Furthermore, the local symmetries are generalized to the systems as a many body treatment performed by Matsen.

By means of the SPG function which is associated with an extreme point of the set of N-representable second-order reduced density matrices, an attempt is made to perform the calculations of the ground states of some atoms with four electrons such as Be. The results show that the SPG function is as suitable as the well-known AGP function for approximating the ground states of atoms and molecules.

Unitary transformations are performed with respect to three Lie group chains in quasispin schemes that are involved in the study of three different calculation schemes in ligand field theory. The unitary transformations hold true for either molecular or atomic orbitals being taken as the starting point. As a result, unitary transformations with respect to matrix elements are accomplished as well.

In this paper, the unitarily invariant decomposition of Hermitian operators is performed by means of irreducible tensor operators to give the explicit expression of the coupling coefficients for [1m] X [r-n] [2s, 1t] with respect to the group structure with the Gel'fand chain of subgroups .

Two small groups (E, σν) and (E, C2) are proposed to describe the orbital symmmetry of the whole reaction paths with respect to suprafacial and antarafacial sigmatropic rearrangements. Furthermore, the symmetries of the two small groups are extended to the systems as a many body treatment performed by Matsen.

The unitarily invariant decomposition of Hermitian operators is performed by means of Lie algebra.