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Kevin M. Lefrancois-Gagnon Robert C. Mawhinney 《Journal of computational chemistry》2020,41(29):2485-2503
The quantum theory of atoms in molecules (QTAIM) provides a theoretical foundation to determine the properties of functional groups through additive atomic contributions. Many studies have used QTAIM in their analyses with a variety of electronic structure methods, but it is unknown if the properties measured using one model chemistry, the combination of the electronic structure method and basis set, can be compared to those measured by another. Here, we evaluate the sensitivity of QTAIM functional group and bond critical point properties using six functionals and seven basis sets. High-level B2PLYPD3-BJ/aug-cc-pV5Z reference values are provided for 116 functional groups and the property sensitivity with respect to these values are evaluated based on absolute deviations and by assessing linear relationships. Functional group properties, including charges, dipoles, quadrupoles and volumes, were found to be mostly insensitive to choice of computational model chemistry. However, due to structural and topological inconsistencies, the 6-31G(d) basis set is not recommended for use. Bond critical point properties varied with choice of model chemistry, but models incorporating hybrid functionals and triple-ζ basis sets provided values suitable for use in regression studies. 相似文献
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The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe). 相似文献
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Substituent effects are ubiquitous in chemistry and the most fundamental is the inductive effect. In this study, the so-called inductive effect was probed in derivatives of bicyclo[1.1.1]pentane-1-carboxylic acid using the isodesmic reaction energy of the acid-base deprotonation, calculated at the PBE0/6-31++G(d,p) level of theory (used throughout). Although structure, molecular orbitals, and nuclear magnetic shielding parameters are discussed, the main focus of this study is the use of the quantum theory of atoms in molecules to analyze the electron density distribution. It was observed that the effect propagates via the manipulation of atomic dipole moments controlled by that of the substituent. As the dipole moment conforms to the principle of atomic transferability, it is found that the substituent dipole determined in simple systems (e.g., R-H) can be used to describe the effect upon the bicyclo[1.1.1]pentane-1-carboxylic acid system. 相似文献
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Christ NH Dawson C Izubuchi T Jung C Liu Q Mawhinney RD Sachrajda CT Soni A Zhou R;RBC UKQCD Collaborations 《Physical review letters》2010,105(24):241601
The large mass of the ninth pseudoscalar meson, the η', is believed to arise from the combined effects of the axial anomaly and the gauge field topology present in QCD. We report a realistic, 2+1-flavor, lattice QCD calculation of the η and η' masses and mixing which confirms this picture. The physical eigenstates show small octet-singlet mixing with a mixing angle of θ=-14.1(2.8)°. Extrapolation to the physical light quark mass gives, with statistical errors only, mη=573(6) MeV and mη'=947(142) MeV, consistent with the experimental values of 548 and 958 MeV. 相似文献
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The title compound, lithium hexamethyldisilazide (LiHMDS), has been studied using modern quantum-chemical methods in the form of the B3LYP approach. Monomers, dimers, trimers, and tetramers, microsolvated with up to four THF molecules have been considered. The choice of model complex is seen to be important-for instance, the simpler water molecule is shown to be an inappropriate substitute for the THF solvent. Calculated lithium NMR shieldings are reported, but by themselves, they seem to be insufficient for unequivocal assignments of the different species. The energetics of aggregation and solvation have been studied. Temperature effects are seen to be important, and the degrees of solvation and aggregation are higher at 0 K than at 298 K. The highest degree of THF solvation for the monomer and dimer is found to be three (0 K) and two (298 K), respectively. The highest possible degree of aggregation for unsolvated LiHMDS is four. However, in nonpolar solvents, formation of the LiHDMS dimer from the trimer is thermodynamically preferred. The pathway is likely to involve an intermediate tetramer. In THF solution, di-solvated monomers and dimers are the most likely species. 相似文献
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Douglas B. Mawhinney Fernando L. Rosario-OrtizSeungyun Baik Brett J. VanderfordShane A. Snyder 《Journal of chromatography. A》2009,1216(9):1319-1324
Fulvic acid standards from Suwannee River, Pony Lake, Elliot Soil, Waskish Peat, and Nordic Reservoir were characterized by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) operating in negative electrospray ionization mode. The method employed a commercially available stationary phase that resulted in a distinctive chromatographic peak for each of the fulvic acid samples that differed in width and retention time at peak maximum. The QTOF-MS, operating in TOF mode, revealed that the unique chromatographic peak shapes were the result of the relative fraction of hydrogen and oxygen contained in various fulvic acid components. Those species that contained larger amount of hydrogen displayed a larger mass defect and were retained longer on the LC column, indicating reduced polarity. This is supported by a reduction in the degree of fragmentation related to polar functional groups as the mass defect and retention time increased. Lastly, the analysis of even and odd mass (at m/z 1 greater) ion intensity ratios revealed a correlation to the percent nitrogen of the various standards. 相似文献
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T P Mawhinney 《Journal of chromatography. A》1986,351(1):91-102
A gas-liquid chromatographic procedure is described which will concomitantly separate and quantitate N-acetylglucosamine, N-acetylgalactosamine, N-acetylglucosaminitol and N-acetylgalactosaminitol in a single analytical run. The hexosamines, as their O-methyloximes, and the hexosaminitols can be separated as either their per-O-acetylated or per-O-trimethylsilylated derivatives. This method is particularly useful with samples that possess both N-acetylhexosaminitols and N-acetylhexosamines as are seen with N-linked oligosaccharides that are cleaved from glycoproteins by alkaline borohydride treatment. This procedure demonstrates a range of acceptable linearity of 1-1000 nmoles for each type of amino sugar. 相似文献
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