SCF MO Research Articles

Adsorption of small molecules on the anatase(1 0 0) surface

The adsorption of NH 3, H 2O, and NO on the (1 0 0) surface of TiO 2 anatase is studied with the semiempirical SCF MO method MSINDO. The (1 0 0) surface is modeled with clusters (TiO 2) n (H 2O) m ( n=33–132, m=17–48) where H and OH groups serve stoichiometrically for saturation. Fivefold coordinated titanium surface atoms, which are Lewis acid sites, are considered as adsorption sites, and the effect of cluster size and surface relaxation on the calculated adsorption energies and geometries is investigated. Only a small dependence on the cluster size and on surface relaxation is found for the adsorption energy. By comparison with experiment and ab initio and density functional theory calculations it is shown that MSINDO can reproduce literature data with satisfactory accuracy.

Adsorption of NO, NH3 and H2O on V2O5/TiO2 catalysts

The adsorption of small molecules NO, NH3 and H2O on V2O5/TiO2 catalysts is studied with the semiempirical SCF MO method MSINDO as pre-stage for the selective catalytic reduction of NO. The mixed catalyst is represented by hydrogen-terminated cluster models. The local arrangement of the cluster atoms is in accordance with available experimental information. Partial relaxation of cluster atoms near the adsorption sites is taken into account. Calculated adsorption energies are compared with experimental literature data. Rapid convergence of computed properties with cluster size is observed. A possible reaction mechanism for the catalytic reduction of NO with NH3 and O2 is outlined.

Effect of Coulomb charge on properties of arsenic vacancy in GaAs-based quantum dots

Structural and electronic characteristics of neutral, positive- and negative charged arsenic vacancies in gallium arsenide based quantum dots (QDs) have been calculated using the nonempirical SCF MO LCAO method within the framework of the cluster approach. The cluster model consisting of 118 atoms was used. It was determined that the change of a charge state of the arsenic vacancy in gallium arsenide cluster leads to a barrier free reconstruction of the defect structure. This reconstruction is revealed as a change of the position of gallium atoms surrounding the vacancy and a redistribution of atom charges in the gallium arsenide cluster. The neutral, positive and negative charged defects can be attributed to the Ev+0.24,Ev+0.20 and Ev+0.50eV QD band gap levels respectively.

AM1 Study of the Conformational Properties of Bicyclo[3.3.3]Undecane and its N-Bridgehead Derivatives

AM1 semiempirical SCF MO calculations show that the BC conformation is the most stable form of bicyclo[3.3.3]undecane (1) and its N-bridgehead derivatives (2 and 3), whereas the corresponding BB conformations are calculated to be from 4.3 kcal/mol in (3) to 7.1 kcal/mol in (1) higher in energy.

Structural Investigation and Preparation of 14-alkyl-14H-dibenzo[a,j]xanthenes revised

높은 순도의 14-알킬-14H-다이벤조[a,j]잔텐의 합성법과 AM1 SCF MO 계산을 보고하였다. Prepartion of the title compounds at 0-5<TEX>$^{\circ}C$</TEX> is reported along with their AM1 SCF MO calculations. The advantage of this procedure is the hight purity of the produ cts.

Luminescence Properties of Strained GaN Epilayers and Spatial Configurations of Silicon Impurity and Related Defects

Near-band-edge photoluminescence and reflection spectra have been investigated in GaN grown on Si and Al2O3 substrates. It has been found that the doping of GaN both with Si and Mg reduces the value of compressive strain in GaN/Al2O3. In GaN/Si, no evidences of the crossover of A and B excitonic resonance positions with increasing tensile strain was observed. The calculations using the non-empirical SCF MO LCAO method showed that the SiGa impurity may lead to an increase of the effective c/a lattice constant ratio, while SiN having greater formation energy produces a lattice relaxation which does not change the c/a ratio significantly. These results are in agreement with experimental observations of decreasing compressive strain in GaN:Si/Al2O3 and increasing tensile strain up to the cracking in GaN:Si/Si.

Synthesis of 5‐R‐3‐Diphenylmethylene‐2,3‐dihydro‐2‐furanones from 5‐Substituted 2,3‐Dihydro‐2,3‐furandiones and Phenylbenzoyldiazomethane.

3-Reactions of 5-aryl, 5-heteryl, and 5-styryl-2,3-dihydro-2,3-furandiones with phenylbenzoyldiazomethane gave rise to 5-substituted 3-dipenylmethylene-2,3-dihydro2-furanones. The possible intermediates and reaction products were investigated by semiempirical SCF MO LCAO method in AM1 approximation.

Geometrical Structures and Magnetic Properties of Trinaphtho[abc,ghi,mno][18]annulene and its congeners

Pariser–Parr–Pople-type SCF MO and semiempirical magnetic-susceptibility calculations show that trinaphtho[ abc,ghi,mno]- and two kinds of triazuleno[ abc,ghi,mno][18]annulenes have large diamagnetic susceptibilities and aromatic-islands structures in which three naphthalenes or three azulenes are linked by three olefinic bridges, whereas tripentaleno[ abc,ghi,mno]- and triheptaleno[ abc,ghi,mno][18]annulenes have small diamagnetic susceptibilities and polyolefine structures where bond alternations are distributed all over their molecular planes.

Optimal methods for calculation of the amount of intermolecular electron transfer

In order to determine the optimal methodology for evaluation of the magnitude of intermolecular charge transfer, several methods have been examined: Mulliken population, natural population analysis, atoms in molecules (AIM) as well as charges from electrostatic potentials using a grid-based method (Chelp and Chelpg) procedures using a series of correlation consistent cc-pVXZ (X=D, T, Q) basis sets within LCAO MO SCF, MP2, DFT, and coupled cluster theory levels. In contrast to previous nonconclusive comparative studies, the present calculations reveal close matching of the recently available experimental data for six Lewis acid-base adducts with theoretical values derived from the Chelpg approach, whereas for the remaining methods relative errors are almost doubled. On the other hand, AIM and Chelpg results display the best linear correlation coefficients with the experimental data. Since reasonably accurate Chelpg results could be already obtained with SCF or DFT B3LYP methods using cc-pVDZ, such an approach opens the way to study intermolecular charge transfer in larger molecular systems. Preliminary results obtained within cc-pVDZ basis set and B3LYP functional for pyridine-SO3 complex do not exceed relative error limits observed for other smaller complexes. Analysis of corresponding interaction energy components calculated consistently in the dimer basis set indicates significant role of electrostatic, exchange and delocalization contributions, with rather negligible correlation term. In contrast to previous findings, the experimentally observed amount of transferred charge seems not to correlate with any interaction energy term.

Reexamination of the Symmetry Rule for Bond Distortions in Conjugated Hydrocarbons

Pariser–Parr–Pople-type SCF MO calculations with the electron correlation effect given by the Brillouin-Wigner second-order perturbation method with Epstein–Nesbet energy denominators and by the Pople–Seeger–Krishnan correction show that the symmetry rule for bond distortions in conjugated hydrocarbons is effective for predicting the geometrical structures of [4 n+2]annulenes.

Adsorption of small molecules on the V 2O 5( [formula omitted]) surface

The adsorption of H, NH 3, H 2O, and NO on the (0 0 1) surface of vanadium pentoxide is studied with the semi-empirical SCF MO method MSINDO. The (0 0 1) surface is modeled with H and OH saturated clusters (V 2O 5) n (H 2O) m ( n=24–54, m=20–40). Different adsorption sites are considered, and the effect of cluster size and surface relaxation on the calculated adsorption energies and geometries is investigated. A slight dependence on the cluster size is found for the adsorption energy, while there is a pronounced effect of surface relaxation. This is in qualitative agreement with previous theoretical studies of the V 2O 5(0 0 1) surface. The absolute values of the adsorption energies for most sites are comparable to the results of previous density functional theory calculations, indicating that MSINDO is a reliable tool for studies of surface properties of vanadium pentoxide.

Reactivity of molecular oxygen on the surface of ionic crystals

A possibility of multiplicity change for ground-state molecular oxygen adsorbed on the surface of regular and doped broad-gap ionic crystals was considered in the framework of cluster approximation by using SCF MO LCAO quantum chemical methods [semiempirical INDO approximation and ab initio calculation with the 6-311G** basis set taking into account the correlation effects on the level of second-order Meller–Plesset perturbation theory (MP2)]. The formation energetics of cyclic products of addition reactions of dioxygen in different multiplet states to furan and cis-butadiene in the gas phase and on the surface of ionic crystals was considered. (These reactions are typical for the O2 singlet state in the gas phase.) It is shown that the presence of sites with high effective charge on the crystal surface can result in a situation not requiring, as in the gas phase, multiplicity change in the transition of a system from an initial to the final state, which can significantly affect the kinetic parameters of the reactions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Reactivity of molecular oxygen on the surface of ionic crystals

AbstractA possibility of multiplicity change for ground‐state molecular oxygen adsorbed on the surface of regular and doped broad‐gap ionic crystals was considered in the framework of cluster approximation by using SCF MO LCAO quantum chemical methods [semiempirical INDO approximation and ab initio calculation with the 6‐311G** basis set taking into account the correlation effects on the level of second‐order Meller–Plesset perturbation theory (MP2)]. The formation energetics of cyclic products of addition reactions of dioxygen in different multiplet states to furan and cis‐butadiene in the gas phase and on the surface of ionic crystals was considered. (These reactions are typical for the O2 singlet state in the gas phase.) It is shown that the presence of sites with high effective charge on the crystal surface can result in a situation not requiring, as in the gas phase, multiplicity change in the transition of a system from an initial to the final state, which can significantly affect the kinetic parameters of the reactions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Ab initio calculations and vibrational spectra of CH3SC=CH and CH3SC=CSCH3

Methylthio- (MTE) and bis-methylthioethyne (BMTE) molecules are calculated by the SCF MO method (geometry optimization, basis set 6–31G*/MP2). The calculated internal rotation barriers of methyl groups are 7.12 kJ/lmole for MTE and 12.86 kJ/mole for BMTE (both groups are simultaneously rotated). The s-gosh-orientation of the thiomethyl fragments corresponds to a stable conformation of BMTE. The estimated values of the s-cis- and s-trans-barriers of mutual rotation of SCH3 groups about the axis of the C≡C bond are 13.61 and 12.54 kJ/mole, respectively. Conformationally sensitive MOs and vibration frequencies are established. An analysis of the experimental IR absorption and Raman spectra and the calculated vibrational spectrum makes it possible to conclude that in the liquid phase the BMTE molecules also have an s-gosh-conformation.

Synthesis of 5-R-3-diphenylmethylene-2,3-dihydro-2-furanones from 5-substituted 2,3-dihydro-2,3-furandiones and phenylbenzoyldiazomethane

3-Reactions of 5-aryl, 5-heteryl, and 5-styryl-2,3-dihydro-2,3-furandiones with phenylbenzoyldiazomethane gave rise to 5-substituted 3-dipenylmethylene-2,3-dihydro2-furanones. The possible intermediates and reaction products were investigated by semiempirical SCF MO LCAO method in AM1 approximation.

Ab initio and density functional theory calculations of the dipole polarizability and the second dipole hyperpolarizability of benzene

AbstractThe linear dipole polarizability α and nonlinear second dipole hyperpolarizability γ of benzene were calculated using the ab initio SCF–MO restricted Hartree–Fock (HF) method. The coupled perturbed HF and time‐dependent HF (TDHF) methods were used for the evaluation of the static and dynamic properties, respectively. The TDHF approach was applied at different optical frequencies, and the second hyperpolarizability γ was evaluated for different optical processes. Electron correlation was taken into account by using the Møller–Plesset perturbation theory (MP2) and the density functional theory B3LYP hybrid approach, with a finite field method, with electric fields of ±0.01, ±0.02, ±0.03, and ±0.04 a.u. used. Benzene was assumed to have a D6h geometry, and the standard STO/6‐31+G(d,p) (A) and optimized STO/6‐31+G(d*,p) (B) basis sets were employed for the calculations. In the optimized basis set, the d exponent of the C atomic function was varied in order to obtain a maximum static benzene γ at the TDHF level of theory. This optimized basis set was able to gives values for the (hyper)polarizabilities of benzene that agree excellently with experimental results and previous calculations. The calculated properties were analyzed in terms of the Laplacian of the electron density calculated using the atoms in molecules method due to Bader. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Physicochemical properties of 1,2-diacylhydrazines derived from aliphatic carboxylic acids

The solubility and resistance to oxidation and hydrolysis of 1,2-diacylhydrazines derived from acetic, propionic, butyric, and valeric acids were studied in view of possible application of these compounds for concentrating nonferrous metals. The pK1 and pK2 values of the 1,2-diacylhydrazines were determined. The stability of conformers and the electron density distribution in the coordination-active moiety were estimated by SCF MO LCAO semiempirical calculations in the MNDO-PM3 approximation.

Insertion of the Al Atom into Alkyl Ethers: Semiempirical SCF MO and Matrix Isolation ESR Study

The insertion process of the Al atom into trimethylene oxide (TMO) and that into dimethyl ether (DME) were examined by a semiempirical SCF molecular orbital method (AM1) and by matrix isolation ESR spectroscopy. The MO study revealed the three step process: (1) an approach of the Al atom toward the ethereal oxygen along the C2v axis of the molecule driven by a favorable overlap between the aluminum SOMO (the 3pz orbital) and the LUMO of the molecule of A1 symmetry, (2) formation of the Al−O dative bond with concurrent scission of one of the C−O bonds, and (3) completion of the process by the three-electron bonding scheme between the unpaired electron on the alkyl terminus and the lone pair electrons on Al. The MO study also revealed that the process would be spontaneous for the Al/TMO system, but for the Al/DME system, there existed a barrier of ∼8 kcal/mol for the onset of the methyl group cleavage from the dative complex Al:O(CH3)2. The MO study also revealed that, in the Al/DME case, the insertion product CH3−Al−O−CH3 of the cis conformation was initially formed but it might readily convert to the more stable trans form. The ESR study revealed that the Al atom insertion into TMO occurred spontaneously. Well-resolved spectra of the expected insertion radical were observed. In the case of DME, the ESR study revealed the presence of both the intermediate dative complex and the final insertion product in the as-prepared matrix. When the matrix was subsequently irradiated with red light (λ = 700 ± 50 nm), the dative complex resumed the process and converted to the insertion product. The insertion radicals of both the cis and trans forms were observed in the argon system, but only the more stable trans radical was observed in the neon system.

AM1 study of conformational properties of Z, Z-, E, E- and E, Z-cyclodeca-1,6-diene

An investigation employing the AM1 semiempirical SCF MO method to calculate structure optimization and conformational interconversion pathways for the three geometrical isomers of cyclodeca-1,6-diene has been undertaken. The Z, Z-isomer is calculated to be 10.3 kJ mol −1 more stable than the E, E-isomer, while the E, Z-isomer is 13.3 kJ mol −1 less stable than the Z, Z-isomer. A chair conformation with C 2 h symmetry is found to be the most stable geometry for Z, Z-cyclodeca-1,6-diene ( 1). The boat form, with C 2 v symmetry, is only 3.5 kJ mol −1 less stable than the chair conformer. Conformational interconversion of these forms requires 52 kJ mol −1. The crown form of the parallel family of E, E-cyclodeca-1,6-diene ( 2) is 7.4 kJ mol −1 more stable than the plane-symmetrical chair–chair–boat geometry. Two axial-symmetrical conformations are found for the crossed family of 2. The twist-boat conformation, with a nonintersecting C 2 axis, is calculated to be 10.3 kJ mol −1 less stable than the crown conformation. The unsymmetrical boat–chair ( 3-BC) conformation of E, Z-cyclodeca-1,6-diene ( 3) is calculated to be 16.6 kJ mol −1 more stable than the axial-symmetrical twist form. The interconversion of 3-TC and twist conformations take place via an unsymmetrical transition state, which is 45.6 kJ mol −1 less stable than 3-TC. The barrier for swiveling of the trans double bond through the unsaturated bridge in compounds 2 and 3 is calculated to be 102.5 and 61.9 kJ mol −1, respectively.

Direct semiclassical simulation of photochemical processes with semiempirical wave functions

We describe a new method for the simulation of excited state dynamics, based on classical trajectories and surface hopping, with direct semiempirical calculation of the electronic wave functions and potential energy surfaces (DTSH method). Semiempirical self-consistent-field molecular orbitals (SCF MO’s) are computed with geometry-dependent occupation numbers, in order to ensure correct homolytic dissociation, fragment orbital degeneracy, and partial optimization of the lowest virtuals. Electronic wave functions are of the MO active space configuration interaction (CI) type, for which analytic energy gradients have been implemented. The time-dependent electronic wave function is propagated by means of a local diabatization algorithm which is inherently stable also in the case of surface crossings. The method is tested for the problem of excited ethylene nonadiabatic dynamics, and the results are compared with recent quantum mechanical calculations.