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Initio Theory (initio + theory)

Distribution by Scientific Domains
Chemistry75%

Kinds of Initio Theory

  • ab initio theory
    		•

    Selected Abstracts

    Structures and Properties of Stable Al4, Al4+, and Al4 - Comparatively Studied by ab Initio Theories

    CHEMINFORM, Issue 40 2007
    Y. L. Zhao
    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]

    Interactions of the "piano-stool" [ruthenium(II) (,6 -arene)(en)CL]+ complexes with water and nucleobases; ab initio and DFT study

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2009
    k Futera
    Abstract Piano stool ruthenium complexes of the composition [Ru(II)(,6 -arene)(en)Cl]+/2+ (en = ethylenediamine) represent an emerging class of cisplatin-analogue anticancer drug candidates. In this study, we use computational quantum chemistry to characterize the structure, stability and reactivity of these compounds. All these structures were optimized at DFT(B3LYP)/6-31G(d) level and their single point properties were determined by the MP2/6-31++G(2df,2pd) method. Thermodynamic parameters and rate constants were determined for the aquation process, as a replacement of the initial chloro ligand by water and subsequent exchange reaction of aqua ligand by nucleobases. The computations were carried out at several levels of DFT and ab initio theories (B3LYP, MP2 and CCSD) utilizing a range of bases sets (from 6-31G(d) to aug-cc-pVQZ). Excellent agreement with experimental results for aquation process was obtained at the CCSD level and reasonable match was achieved also with the B3LYP/6-31++G(2df,2pd) method. This level was used also for nucleobase-water exchange reaction where a smaller rate constant for guanine exchange was found in comparison with adenine. Although adenine follows a simple replacement mechanism, guanine complex passes by a two-step mechanism. At first, Ru-O6(G) adduct is formed, which is transformed through a chelate TS2 to the Ru-N7(G) final complex. In case of guanine, the exchange reaction is more favorable thermodynamically (releasing in total by about 8 kcal/mol) but according to our results, the rate constant for guanine substitution is slightly smaller than the analogous constant in adenine case when reaction course from local minimum is considered. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source]

    Computational study of the chair,chair interconversion and stereoelectronic interactions in 1,2,3-trithiacyclo-hexane (1,2,3-trithiane)

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2004
    Fillmore Freeman
    Abstract Ab initio theory, density functional theory (DFT) and Møller,Plesset perturbation theory (MP2) with the 6,31G(d), 6,31++G(d), 6,31G(d,p), 6,31+G(d,p), 6,31++G(d,p), 6,311G(d,p) and 6,311+G(d,p) basis sets were used to study stereoelectronic hyperconjugative interactions and the mechanism of the chair,chair conformational interconversion in 1,2,3-trithiacyclohexane (1,2,3-trithiane). The relative energies, enthalpies, entropies, free energies and structural parameters of the chair, 1,4-twist and 2,5-twist conformers, a distorted 1,4-boat transition state and a 2,5-boat transition state were calculated. The HF calculated energy difference (,E) between the chair conformer of 1,2,3-trithiane and the distorted 1,4-boat transition state was 10.59,kcal,mol,1 (1 kcal=4.184,kJ). The 1,4-twist conformer and the 2,5-boat transition state are close in energy, as are the 2,5-twist conformer and the distorted 1,4-boat transition state. B3LYP/6,311+G(d,p) calculated the chair conformer of 1,2,3-trithiane to be 5.83, 10.09, and 5.96,kcal,mol,1, respectively, lower in energy than the 1,4-twist conformer, 2,5-twist conformer and 2,5-boat transition state. Intrinsic reaction coordinate (IRC) calculations were used to connect the transition state between the chair conformer and the 1,4-twist conformer. B3LYP/6,31+G(d,p) and B3LYP/6,311+G(d,p) calculated this transition state to be 14.25,kcal,mol,1 higher in energy than the chair conformer. In the chair conformer, the respective C4,H and C6,H bond lengths are equal, but the C5,Heq bond is longer than the C5,Hax bond. In the 1,4-twist conformer, the C4,Hiso bond lengths are equal, the C5,H,eq bond is longer than the C5,H,ax bond and the C6,H bond lengths are equal. In the 2,5-twist conformer, equal C,H bond lengths are found at C4 and at C5, but the C6,H,eq bond is longer than the C6,H,ax bond. Copyright © 2003 John Wiley & Sons, Ltd. Additional material for this paper is available in Wiley Intersciene [source]

    Ab initio theory of exchange interactions in itinerant magnets

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
    I. Turek
    Abstract The paper reviews an ab initio two-step procedure to determine thermodynamic properties of itinerant magnets. In the first step, the selfconsistent electronic structure of a system is calculated using the tight-binding linear muffin-tin orbital method combined with Green function techniques. In the second step, the parameters of the effective classical Heisenberg Hamiltonian are determined using the magnetic force theorem and they are employed in subsequent evaluation of magnon spectra, the spin-wave stiffness constants and the Curie/Néel temperatures. Applicability of the developed scheme is illustrated by investigations of selected properties of 3d metals Fe, Co, and Ni, diluted magnetic semiconductors (Ga,Mn)As, and 4f metals Gd and Eu. [source]