The structures, stabilities, and electronic properties of the single-vacancy-defected fullerenes, C-60 and C-70, and the single- and double-vacancy-defected single-walled carbon nanotubes (SWCNTs) were studied within density functional theory. The isomerization barriers for the single-vacancy-defected C,, on the triplet potential energy surface (PES) are lower than those on the singlet PES. The symmetric double-vacancy-defected (10,0) SWCNT is the most stable one among the models investigated. According to the analyses of frontier molecular orbitals (FMOs), nature bond orbitals, and local density of states, introduction of vacancy on the SWCNT decreases the band gap of semiconducting SWCNT, increases the band gap of conducting SWCNT, destructs the pi conjugation of the FMOs, and gives rise to enhanced chemical activity. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 3441-3456, 2009

}, keywords = {BUCKMINSTERFULLERENE, C-60, COMPUTATIONS, CONDUCTANCE, density, EXCHANGE, FULLERENE, GENERALIZED GRADIENT APPROXIMATION, GROWTH, INHIBITION, OXIDES, single-walled carbon nanotube, vacancy defect}, isbn = {0020-7608}, url = {The corrected Hohenberg-Kohn-Sham and corrected Harris total energy functionals recently proposed [B. Zhou and Y. A. Wang, J. Chem. Phys. 128, 084101 (2008)] have been generalized to the Hartree-Fock method. We have tested the functionals on a few molecular systems and found them to be very useful in accelerating the convergence of the total energy during a self-consistent field process.

}, keywords = {AB-INITIO, CRC, density, density functional theory, ELECTRON-GAS, EXTREMAL PROPERTIES, HF calculations, iterative methods, PERTURBATION THEORY, SCF calculations, SOLIDS, total energy}, isbn = {0021-9606}, url = {Molecular structure of 1-chloro-1,1-difluoro-pentane-2,4-dione (monochlorodifluoro-acetylacetone, CDFAA) has been investigated by means of ab initio and Density Functional Theory (DFT) calculations and the results were compared with those of 1,1,1-trifluoropentane-2,4-dione (trifluoro-acetylacetone, TFAA). The harmonic vibrational frequencies of the two most stable cis-enol forms were calculated at the 133LYP level of theory using 6-3 1 G** and 6-311 ++G** basis sets. We also calculated the anharmonic frequencies at the B3LYP/6-31G** level of theory for these two stable cis-enol isomers. The calculated frequencies and the Raman and IR intensities were compared with the experimental results. The energy difference between the two stable cis-enol forms, calculated at the MP2/6-31G** level, is only 3.42 U/mol. The observed vibrational frequencies and intensities in the gas phase are in excellent agreement with the corresponding values calculated for the two most stable conformers. However, the observed IR and Raman frequencies also indicate coexisting of both tautomers in the liquid phase and in solution. According to the theoretical calculations, at the B3LYP/6-31 1++G** level, the hydrogen bond strength for the most stable conformer is 54.45 U/mol, about 2.4 kJ/mol less than that of the corresponding conformer of TFAA. These results are in agreement with the obtained experimental data. (C) 2007 Elsevier B.V. All rights reserved.

}, keywords = {1-chloro-1, 1-difluoro-pentane-2, 4-dione, AB-INITIO, anharmonicity, BETA-DIKETONES, density, ELECTRON-DIFFRACTION, ENERGY, EQUILIBRIUM, functional theory, HEXAFLUORO-ACETYLACETONE, intramolecular hydrogen bond, MALONALDEHYDE, MOLECULAR-STRUCTURE, TAUTOMERISM, vibrational spectra}, isbn = {0022-2860}, url = {In this work, we applied a two-layered ONIOM (B3LYP/6-31G(d):UFF) method to study the reaction of nitric oxides with a 5-1DB defect on the sidewall of the single-walled carbon nanotube (SWCNT). We have chosen a suitable ONIOM model for the calculation of the SWCNT based on the analyses of the frontier molecular orbitals,, local density of states, and natural bond orbitals. Our calculations clearly indicate that the 5-1DB defect is the chemically active center of the SWCNT. In the reaction of nitric oxides with the defected SWCNT, the 5-1DB defect site can capture a nitrogen atom from nitric oxides, yielding the N-substitutionally doped SWCNT. We have explored the reaction pathway in detail. Our work verifies the chemical reactivity of the 5-1DB defects of the SWCNTs, indicates that the 5-1DB defect is a possible site for the functionalization of the SWCNTs, and demonstrates a possible way to fabricate position controllable substitutionally doped SWCNTs with a low doping concentration under mild conditions via some simple chemical reactions.

}, keywords = {AB-INITIO, BORON, chemisorption, density, DOPED CARBON, MOLECULAR-MECHANICS, NITROGEN, ONIOM, OPTIMIZATION, sensors}, isbn = {1520-6106}, url = {Measurements of the outermost valence electron orbital momentum profiles of the open shell molecules NO, O-2 and NO2 have been obtained using electron momentum spectroscopy (EMS). The presently reported experimental momentum profiles of NO and O-2 display much improved statistics compared with previously published EMS results while the data for the HOMO of NO, is the first reported. In the case of NO, the present measurements are considerably different from previous results and these differences appear to be due to the presence of NO2 impurities in the previous work. The EMS measurements provide a stringent test of basis set effects and the quality of ab initio methods in the description of these open shell systems. The experimental momentum profiles have been compared with theoretical spherically averaged momentum profiles from several basis sets calculated at the level of the target Hartree-Fock approximation (THFA) with a range of basis sets using both unrestricted Hartree-Fock (UHF) and restricted open shell Hartree-Fock (ROHF) methods. Various configuration interaction calculations such as multi-reference singles and doubles configuration interaction (MRSD-CI), averaged coupled pair functional (ACPF) and quasi-degenerate variational perturbation theory (QDVPT) calculations of the full ion-neutral overlap amplitude have also been compared to experiment to investigate the effects of electron correlation and relaxation. The experimental momentum profiles have further been compared to calculations at the level of the target Kohn-Sham approximation (TKSA) using density functional theory (DFT) with the local density approximation and also with gradient corrected exchange-correlation potentials. In addition to momentum profiles, other electronic properties such as total energies, dipole moments, quadrupole moments and values of the electronic spatial extent have been calculated by the various theoretical methods and compared to experimental values.

}, keywords = {CORRELATED WAVEFUNCTIONS, CORRELATION ENERGIES, density, DIPOLE-MOMENT, EXCHANGE-ENERGY, GAUSSIAN-BASIS SETS, NITRIC-OXIDE, VALENCE ORBITALS, VARIATIONAL PERTURBATION-THEORY, WAVE-FUNCTIONS}, isbn = {0301-0104}, url = {