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Initio Investigation (initio + investigation)
Kinds of Initio Investigation Selected AbstractsSpin-Orbit Ab Initio Investigation of the Ultraviolet Photolysis of DiiodomethaneCHEMPHYSCHEM, Issue 6 2007Ya-Jun Liu Dr. Abstract The UV photodissociation (<5 eV) of diiodomethane (CH2I2) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH2I2 and CH2II lead to geminate-radical products, CH2I,.+I(2P3/2) or CH2I,.+ I*(2P1/2). The recombination process from CH2II to CH2I2 is explained by an isomerization process and a secondary photodissociation reaction of CH2II. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH2II species. [source] ChemInform Abstract: An ab initio Investigation of Bismuth Hydration.CHEMINFORM, Issue 12 2008Cory C. Pye Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Ab initio Investigation of the Electronic Structures of Ternary Germanides CeRhGe and CeIrGe.CHEMINFORM, Issue 31 2007S. F. Matar Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Ab initio Investigation of the Electronic and Geometric Structure of Magnesium Diboride, MgB2.CHEMINFORM, Issue 7 2006Demeter Tzeli Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF. [source] ChemInform Abstract: In Search of Covalently Bound Tetra- and Penta-Oxygen Species: A Photoelectron Spectroscopic and ab initio Investigation of MO4 - and MO5 - (M: Li, Na, K, Cs).CHEMINFORM, Issue 36 2002Hua-Jin Zhai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The Diels,Alder Reaction of Ethene and 1,3-Butadiene: An Extended Multireference ab initio InvestigationCHEMPHYSCHEM, Issue 9 2004Hans Lischka Prof. Dr. Abstract The concerted and stepwise mechanisms of the Diels,Alder reaction between 1,3-butadiene and ethene have been investigated using highly correlated multireference methods (MRAQCC) and extended basis sets. Full MRAQCC geometry optimizations have been performed in all cases. The best estimate for the energy barrier of the Diels,Alder reaction is 22 kcal,mol,1. Anti- and gauche-out minima for the biradical structures and corresponding fragmentation saddle points have been determined. The biradical anti fragmentation saddle point is located 6.5 kcal,mol,1above the concerted saddle point. The gauche-in structure does not correspond to a local minimum, but leads on geometry optimization directly to cyclohexene. [source] Anionic ring-opening polymerization of small phosphorus heterocycles and their borane adducts: An ab initio investigationHETEROATOM CHEMISTRY, Issue 2 2007Michelle L. Coote The kinetics and thermodynamics of anionic ring-opening reactions of phosphiranes, phosphetanes, and phospholanes and their borane adducts have been studied by high-level ab initio procedures. For the free heterocycles, model propagation reactions involving nucleophilic attack by Me2P, at the ring ,-carbon were found to be feasible for the three- and four-membered rings, but not for the five-membered ring. For the borane adducts, nucleophilic attack by Me2(BH3)P, was only facile for the three-membered ring, despite an increased thermodynamic tendency toward ring opening for the borane adducts of both the three- and four-membered rings. The formation constants of the borane adducts of methylphosphirane and methylphosphetane were K = 2.6 × 1013 L mol,1 and K = 1.2 × 1020 L mol,1, respectively. A Marcus analysis of the ring-opening reactions of methylphosphirane, methylphosphetane, and their borane adducts showed that the release of ring strain and an "additional factor" contribute to rate enhancement compared with their strain-free analogues. The additional factor was larger for the three-membered rings than for the four-membered rings and was larger in the free heterocycles than in their borane adducts. The additional factor is complex in origin and appears to reflect an increase in the separation between the bonding and antibonding orbitals of the breaking bond on going from the three-membered rings to the four-membered rings, and on going from the free heterocycles to the borane adducts. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:118,128, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20323 [source] Ab initio investigation of the solvent and electron correlation effects on the geometries and first hyperpolarizabilities of push,pull oligomersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2007Eric A. Perpète Abstract Using the HF and MP2 approaches, we have determined the ground-state geometry and first hyperpolarizability of increasingly long push,pull polyacetylene oligomers. The bulk solvent effects have been assessed at both levels of theory through the Polarizable Continuum Model. For the first hyperpolarizability, the resulting 16 combination of theoretical levels of computation have been compared to evaluate the importance of individual corrections, as well as their additive/ multiplicative character. It turns out that the inclusion of bulk solvent effects is essential for an accurate estimate of the nonlinear optics properties of these push,pull derivatives. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Ab initio investigation on the reaction path and rate for the gas-phase reaction of HO + H2O , H2O + OHJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2003Tadafumi Uchimaru Abstract This article describes an ab initio investigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O , H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen-bonding complexes [HOHOH] and [H2OHO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOHOH] complex, while the OH radical acts as a hydrogen donor in the [H2OHO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS-APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as ,2.1 , ,2.3 and ,4.1 , ,4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2OHO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS-APNO energy evaluations. After fitting the CBS-APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538,1548, 2003 [source] Ab initio investigation of the LiNbO3 (0001) surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Simone Sanna Abstract The polar surfaces of ferroelectric LiNbO3 have been investigated by an ab initio thermodynamical approach. Basing on density functional theory total energy calculations, we discuss the relative stability of a series of candidate surface structures with varying stoichiometry and surface reconstruction in dependence on the chemical environment. We determine the equilibrium geometry for the positively and negatively polarised surfaces and then discuss the influence of different stabilising mechanisms on the preferred terminations. Positive and negative surfaces are found to have different structure, stoichiometry and ionisation energy. The positive surface is found to contain more oxygen than the negative surface at similar conditions. Different stabilisation mechanisms like stoichiometry modification and reconstruction contribute to stabilise the polar surfaces (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||