Interaction of hydrogen atoms with polyatomic molecules studied by means of scattering experiments and hybrid Hartree-Fock plus damped dispersion calculations

1983 ◽  
Vol 87 (15) ◽  
pp. 2772-2780 ◽  
Author(s):  
G. O. Este ◽  
D. G. Knight ◽  
G. Scoles ◽  
U. Valbusa ◽  
F. Grein
Keyword(s):  
Polyatomic Molecules ◽  
Hydrogen Atoms ◽  
Hartree Fock

Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. I. Method

1993 ◽  
Vol 48 (7) ◽  
pp. 829-833
Author(s):  
Wolfhard Koch
Keyword(s):  
Electron Correlation ◽  
Ground State ◽  
Atomic Orbital ◽  
Closed Shell ◽  
Open Shell ◽  
Polyatomic Molecules ◽  
Correlation Effects ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Electronic Ground

Abstract Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.

EMS studies of larger molecules of chemical and biochemical interest

1996 ◽  
Vol 74 (11-12) ◽  
pp. 773-781 ◽  
Author(s):  
J. J. Neville ◽  
Y. Zheng ◽  
B. P. Hollebone ◽  
N. M. Cann ◽  
C. E. Brion ◽  
...  
Keyword(s):  
Density Functional ◽  
Polyatomic Molecules ◽  
Target Compound ◽  
Frontier Orbitals ◽  
Functional Theory ◽  
Electron Momentum ◽  
Hartree Fock ◽  
Electron Momentum Spectroscopy ◽  
Key Factor ◽  
Increased Sensitivity

The challenges involved in extending electron momentum spectroscopy (EMS) studies beyond small polyatomic molecules to more complicated systems are discussed. EMS results for the highest occupied (frontier) molecular orbitals of glycine (NH2CH2COOH) and dimethoxymethane ((CH3O)2CH2) demonstrate possible approaches to overcoming such challenges as closely spaced valence orbitals, low volatility, and the conformational mobility of the target compound. The increased sensitivity available from recently developed multichannel electron momentum spectrometers is a key factor in overcoming these challenges and making such EMS studies feasible. The utility of Kohn–Sham density functional theory (DFT) for EMS calculations on larger molecules such as glycine and dimethoxymethane using the recently formulated target Kohn–Sham approximation is also investigated as experimental momentum profiles are compared with theoretical momentum profiles generated via Kohn–Sham DFT and a range of Hartree–Fock calculations. The Kohn–Sham DFT calculations provide better agreement with experiment for the frontier orbitals of glycine and dimethoxymethane than even the near Hartree–Fock limit results.

Kinetic Isotope and Collision Energy Effects in the Dissociation of Chloride and Bromide Adducts of Aliphatic Alcohols, Benzaldehyde, and 2,4-Pentanedione

2003 ◽  
Vol 56 (5) ◽  
pp. 415 ◽  
Author(s):  
Rodinei Augusti ◽  
Xubin Zheng ◽  
M. Turowski ◽  
R. Graham Cooks
Keyword(s):  
Density Functional ◽  
Collision Energy ◽  
Basis Set ◽  
Cluster Ions ◽  
Basis Sets ◽  
Stable Form ◽  
Triple Quadrupole Mass Spectrometer ◽  
Hydrogen Atoms ◽  
Hartree Fock ◽  
Chloride Adduct

A tandem-in-space triple quadrupole mass spectrometer was used to measure kinetic isotopic effects (KIEs) for the dissociation of chloride and bromide adducts of several compounds that bind halide anions via either hydrogen bonds or by nucleophilic attachment. Two isotopomers of each adduct were simultaneously mass-selected in the first quadrupole and dissociated by collision with argon in the second quadrupole. The KIEs were measured by comparing the extents of dissociation of the lighter versus the heavier isotopomeric adducts. In most cases, lower collision energies and multiple collision conditions favoured larger KIE values, an expected feature of easily dissociated cluster ions considering zero-point energies (ZPEs). The larger chloride adduct of cyclohexanol gave greater KIEs compared with the smaller alcohols, a consequence of slower dissociation due to the larger number of degrees of freedom. Dissociation of the chloride adducts gave greater KIEs than the corresponding bromide adducts, a result that is also consistent with expectations based on ZPEs. Both the chloride and bromide adducts of 2,4-pentanedione, when dissociated at 6 eV collision energy under single-collision conditions, displayed normal KIEs (1.0460 ± 0.0012 and 1.0092 ± 0.0035 respectively). These and the alcohol results were correctly predicted by the ZPEs calculated using commonly applied ab initio Hartree–Fock (HF) and B3LYP density functional theory (DFT) methods with large basis sets (6–311 containing both polarization and diffuse functions). Geometry optimization calculations for the 2,4-pentanedione chloride adduct using either the Restricted Hartree–Fock (RHF) method with a 6–31G* basis set or using the more accurate 6–31++G** method showed that, in the most stable form, the chloride is bonded at multiple sites by a molecule of 2,4-pentanedione. In this structure, chloride binds weakly to both the methylene and the methyl hydrogen atoms. Collision-induced dissociation furnishes chloride and 2,4-pentanedione anion ([M – H]–) as competitive negatively charged products, which is consistent with the proposed structure. It is interesting that the intermolecular KIEs in this study tend to be normal, while intramolecular isotope effects in halides, notably of the type M1Cl+M2 are inverse, as a consequence of the lower ZPEs associated with the heavier isotopomers. The difference in the two systems is that the stronger bonds are found in the products in the case of M1Cl+M2 dissociation but in the reactants in the case of MCl– dissociation.

Quantum Mechanical Study of Clean and H-Covered α-MoO3(100) Surface

2003 ◽  
Vol 02 (02) ◽  
pp. 245-256 ◽  
Author(s):  
A. Sayede ◽  
B. Khelifa ◽  
C. Mathieu ◽  
H. Aourag
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Population Analysis ◽  
Chemical Properties ◽  
Hydrogen Atoms ◽  
Mulliken Population ◽  
Hartree Fock ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Local Electronic Structure

Structure and electronic properties of the α-MoO3(100) surface, as well as H adsorption on the α-MoO3(100) surface have been studied with periodic slab Hartree–Fock calculations. Gradient corrected density functional calculations have been performed in this study. The structure and electronic properties of the (100) surface are in agreement with experimental and previous theoretical results. Local electronic structure near the different surface oxygen sites are analyzed with Mulliken Population Analysis. The oxide is partially ionic and the symmetrically oxygens exhibit more ionic feature while the terminal oxygens are more covalent. Electrostatic potentials show broad negative minima above the terminal oxygen centers, which suggest that electrophilic adparticles, like H, resulting from surface reactions, will be attracted preferentially at these sites. The results of the H adsorption on the (100) surface are interpreted based on charge-transfer interactions between the surface and H species. It is found that terminal oxygen sites are the most stable binding site. Ionic relaxation of the α-MoO3(100) surface for the adsorption of hydrogen has no effect on the chemical properties and hydrogen atoms adsorbed favorably on the α-MoO3(100) surface at full coverage.

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