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Hybrid Density Functional Theory (hybrid + density_functional_theory)
Selected AbstractsDFT study for the heterojunction effect in the precious metal clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Mitsutaka Okumura Abstract In the case of the precious metal catalysts, the precious metal nanoparticles deposited on the several supports exhibit extremely high-catalytic activity for many catalytic reactions. The boundary region between the nanoparticles and the support is one of the active sites in these catalysts. Moreover, the core/shell-type bimetallic nanoparticles also show the high-catalytic activities for several catalytic reactions. In these systems, the electronic states of the surfaces in the clusters are modified by the heterojunction between the two different compositions. Therefore, we investigate the heterojunction effect in these model catalysts, such as precious metal core/shell clusters and Pd supported on single-wall carbon nanotube model cluster, using hybrid density functional theory. From the calculation results, we find that the charge transfer interactions and the variation of the ground spin states in the metal clusters are the characteristics induced by the heterojunction in these model systems. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Theoretical Studies on ortho -Oxidation of Phenols with Dioxygen Mediated by Dicopper Complex: Hints for a Catalyst with the Phenolase Activity of TyrosinaseADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Hiroshi Naka Abstract Theoretical studies on the chemo- and regioselective ortho -oxidation reaction of phenols mediated by a biomimetic (,,,2:,2peroxo)dicopper(II) complex were performed using unrestricted hybrid density functional theory (UB3LYP) calculations, with the aim of providing a guide for the development of new bio-inspired catalysts with the phenolase activity of tyrosinase. Energetic, structural, and electronic analyses suggested the involvement of a side-on (,,,2:,2)-Cu2O2 complex as an active intermediate, and a single electron transfer (SET)-induced electrophilic aromatic substitution mechanism is proposed for the rate-determining CO bond forming process; this is consistent with experimental observations. Moreover, the inherent roles of, and requirement for, two copper ions in this reaction have been elucidated. [source] Dispersion in the Mott insulator UO2: A comparison of photoemission spectroscopy and screened hybrid density functional theory,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Lindsay E. Roy Abstract We present a comparison between the screened hybrid density functional theory of Heyd, Scuseria, and Enzerhof (HSE06) and high-resolution photoemission (PES) measurement on a single crystal of UO2. Angle-resolved photoemission data show a slight dispersion in the f -orbital derived bands in good agreement with the HSE band structure. The effect of spin-orbit coupling on the HSE band gap has also been calculated and found to be negligible. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Parameterization of charge model 3 for AM1, PM3, BLYP, and B3LYPJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2003Jason D. Thompson Abstract We have recently developed a new Class IV charge model for calculating partial atomic charges in molecules. The new model, called Charge Model 3 (CM3), was parameterized for calculations on molecules containing H, Li, C, N, O, F, Si, S, P, Cl, and Br by Hartree,Fock theory and by hybrid density functional theory (DFT) based on the modified Perdew,Wang density functional with several basis sets. In the present article we extend CM3 to semiempirical molecular orbital theory, in particular Austin Model 1 (AM1) and Parameterized Model 3 (PM3), and to the popular BLYP and B3LYP DFT and hybrid DFT methods, respectively. For the BLYP extension, we consider the 6-31G(d) basis set, and for the B3LYP extension, we consider three basis sets: 6-31G(d), 6-31+G(d), and MIDI!6D. We begin with the previous CM3 strategy, which involves 34 parameters for 30 pairs of elements. We then refine the model to improve the charges in compounds that contain N and O. This modification, involving two new parameters, leads to improved dipole moments for amides, bifunctional H, C, N, O compounds, aldehydes, ketones, esters, and carboxylic acids; the improvement for compounds not containing N results from obtaining more physical parameters for carbonyl groups when the OCN conjugation of amides is addressed in the parameterization. In addition, for the PM3 method, we added an additional parameter to improve dipole moments of compounds that contain bonds between C and N. This additional parameter leads to improved accuracy in the dipole moments of aromatic nitrogen heterocycles with five-membered rings. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1291,1304, 2003 [source] Theoretical Studies of Damage to 3,-Uridine Monophosphate Induced by Electron AttachmentCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2008bo Zhang Ass. Abstract Low-energy electrons (LEE) are well known to induce nucleic acid damage. However, the damage mechanisms related to charge state and structural features remain to be explored in detail. In the present work, we have investigated the N1-glycosidic and C3,O(P) bond ruptures of 3,-UMP (UMP=uridine monophosphate) and the protonated form 3,-UMPH with ,1 and zero charge, respectively, based on hybrid density functional theory (DFT) B3,LYP together with the 6-31+G(d,p) basis set. The glycosidic bond breakage reactions of the 3,UMP and 3,UMPH electron adducts are exothermic in both cases, with barrier heights of 19,20,kcal,mol,1 upon inclusion of bulk solvation. The effects of the charge state on the phosphate group are marginal, but the C2,OH group destabilizes the transition structure of glycosidic bond rupture of 3,-UMPH in the gas phase by approximately 5.0,kcal,mol,1. This is in contrast with the C3,O(P) bond ruptures induced by LEE in which the charge state on the phosphate influences the barrier heights and reaction energies considerably. The barrier towards C3,O(P) bond dissociation in the 3,UMP electron adduct is higher in the gas phase than the one corresponding to glycosidic bond rupture and is dramatically influenced by the C2,OH group and bulk salvation, which decreases the barrier to 14.7,kcal,mol,1. For the C3,O(P) bond rupture of the 3,UMPH electron adduct, the reaction is exothermic and the barrier is even lower, 8.2,kcal,mol,1, which is in agreement with recent results for 3,-dTMPH and 5,-dTMPH (dTMPH=deoxythymidine monophosphate). Both the Mulliken atomic charges and unpaired-spin distribution play significant roles in the reactions. [source] Copper(II)-Mediated Aromatic ortho -Hydroxylation: A Hybrid DFT and Ab Initio ExplorationCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Peter Comba Prof. Dr. Abstract Mechanistic pathways for the aromatic hydroxylation by [CuII(L1)(TMAO)(O)], (L1=hippuric acid, TMAO=trimethylamine N -oxide), derived from the ON bond homolysis of its [CuII(L1)(TMAO)2] precursor, were explored by using hybrid density functional theory (B3LYP) and highly correlated ab initio methods (QCISD and CCSD). Published experimental studies suggest that the catalytic reaction is triggered by a terminal copper,oxo species, and a detailed study of electronic structures, bonding, and energetics of the corresponding electromers is presented. Two pathways, a stepwise and a concerted reaction, were considered for the hydroxylation process. The results reveal a clear preference for the concerted pathway, in which the terminal oxygen atom directly attacks the carbon atom of the benzene ring, leading to the ortho -selectively hydroxylated product. Solvent effects were probed by using the PCM and CPCM solvation models, and the PCM model was found to perform better in the present case. Excellent agreement between the experimental and computational results was found, in particular also for changes in reactivity with derivatives of L1. [source] Ethylene Biosynthesis by 1-Aminocyclopropane-1-Carboxylic Acid Oxidase: A DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2006Arianna Bassan Dr. Abstract The reaction catalyzed by the plant enzyme 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) was investigated by using hybrid density functional theory. ACCO belongs to the non-heme iron(II) enzyme superfamily and carries out the bicarbonate-dependent two-electron oxidation of its substrate ACC (1-aminocyclopropane-1-carboxylic acid) concomitant with the reduction of dioxygen and oxidation of a reducing agent probably ascorbate. The reaction gives ethylene, CO2, cyanide and two water molecules. A model including the mononuclear iron complex with ACC in the first coordination sphere was used to study the details of OO bond cleavage and cyclopropane ring opening. Calculations imply that this unusual and complex reaction is triggered by a hydrogen atom abstraction step generating a radical on the amino nitrogen of ACC. Subsequently, cyclopropane ring opening followed by OO bond heterolysis leads to a very reactive iron(IV),oxo intermediate, which decomposes to ethylene and cyanoformate with very low energy barriers. The reaction is assisted by bicarbonate located in the second coordination sphere of the metal. [source] | ||||||||||