Search results for "ab initio"

Theoretical ab initio study of the vinylcarbene-CuO complex: application to last step of the propylene partial oxidation mechanism on Cu2O

1988

Abstract Using non-empirical pseudopotentials, we have performed a theoretical study on the last step of the propylene partial oxidation mechanism, the acrolein desorption from the catalyst surface. To represent the catalyst we have used a simplified model of a catalyst active site. We have study the C 3 H 4 CuO complex, analysing the dissociation process of the oxygenated complex from a metallic centre. The results indicate that this complex dissociates into cis - and trans -acrolein and a metal site, in a process without energetic barrier.

Cluster and Periodic Calculations of the Ethene Protonation Reaction Catalyzed by theta-1 Zeolite: Influence of Method, Model Size, and Structural Co…

2001

The protonation of ethene by three different acid sites of theta-1 zeolite was theoretically studied to analyze the extent and relevance of the following aspects of heterogeneous catalysis: the local geometry of the Bronsted acid site in a particular zeolite, the size of the cluster used to model the catalyst, the degree of geometry relaxation around the active site, and the effects related to medium- and long-range interactions between the reaction site and its environment. It has been found that while the reaction energy is very sensitive to the local geometry of the site, the activation energy is mainly affected by the methodology used and by electrostatic effects on account of the carbo…

An ab initio conformational study on captopril

2003

Abstract Captopril can interact regio- and stereo-specifically with various functional groups present at the active site of angiotensin converting enzyme (ACE). Since no X-ray structure of ACE is available, Captopril, as an ACE inhibitor may be used as a ‘molecular caliper’, to estimate upper and lower bound values for separation d, where the mercaptidic terminal group of the molecule is linked to the enzyme Zn2+ cofactor, while the carboxylate links via an hydrogen bond to the guanidine moiety of an arginine side chain. As the results of this Ab Initio study, the conformations of the dianionic form of the full captopril molecule are reported here.

Precise branching ratios to unbound 12C states from 12N and 12B β-decays

2009

6 pages, 2 tables, 4 figures.--PACS nrs.: 21.45.-v; 23.40.-s; 27.20.+n; 21.60.De.--Printed version published Aug 3, 2009

The bromine nuclear quadrupole moment revisited

2013

For the bromine atom and the hydrogen bromide molecule, we report results for the electric-field gradient at the bromine nucleus based on quantum-chemical calculations. Highly accurate values are obtained by using coupled-cluster methods for the treatment of electron correlation, by minimising remaining basis-set effects through the use of large atomic-orbital sets, and by taking into account relativistic effects. For hydrogen bromide, zero-point vibrational corrections are considered as well. The obtained results for the bromine electric-field gradients are used to derive values for the Br-79 quadrupole moment: 308.1 and 309.3 mb based on data for the bromine atom and hydrogen bromide, res…

Modelowanie metodami ab initio i DFT właściwości spektroskopowych wybranych pochodnych ftalocyjaniny

2017

Odkryte na początku XX wieku ftalocyjaniny to interesująca klasa związków chemicznych. Dzięki obecności cyklicznego polienu spełniającego regułę Huckla struktury chemiczne tych związków są bardzo trwałe, a w pierścieniach benzenowych na obrzeżach tych związków można umieścić podstawniki. Można modyfikować w ten sposób właściwości ftalocyjaniny takie jak rozpuszczalność czy zdolność katalityczną. Jednak najważniejszą cechą tych związków są sprzężone wiązania podwójne, dzięki którym wykazują one absorpcję światła w zakresie widzialnym. Ftalocyjaniny i ich pochodne znajdują zastosowanie między innymi jako barwniki, katalizatory, fotouczulacze, sensory chemiczne i komórki światłoczułe w panelac…

Functionalized Tellurium(II) Thiolates: Tellurium Bis(2-hydroxyethanethiolate) Hydrate, the First H2O–TeII Complex

2000

Relationship between Electron Affinity and Half-Wave Reduction Potential: A Theoretical Study on Cyclic Electron-Acceptor Compounds.

2016

A high-level ab initio protocol to compute accurate electron affinities and half-wave reduction potentials is presented and applied for a series of electron-acceptor compounds with potential interest in organic electronics and redox flow batteries. The comprehensive comparison between the theoretical and experimental electron affinities not only proves the reliability of the theoretical G3(MP2) approach employed but also calls into question certain experimental measurements, which need to be revised. By using the thermodynamic cycle for the one-electron attachment reaction A+e- →A- , theoretical estimates for the first half-wave reduction potential have been computed along the series of ele…

Relevance of the Electronegativity of Boron inη5-Coordinating Ligands: Regioselective Monoalkylation and Monoarylation in Cobaltabisdicarbollide[3,3′…

2003

Regioselective monoalkylation and monoarylation in cobaltabisdicarbollide clusters has been achieved starting from Cs[8-I-3,3'-Co(1,2-C 2 B 9 H 1 0 )(1',2'-C 2 B 9 H 1 1 )] by cross-coupling reactions between a B-I fragment andan appropriate Grignard reagent in the presence of a Pd catalyst and CuT. A considerable number of monoalkylated and monoarylated derivatives have been synthesized, which allowed study of the influence of boron in metallocene-type ligands and the effect of alkyl and aryl substituents on boron in boron anionic clusters. Experimental data from UV/ Vis spectroscopy, E 1 / 2 measurements, and X-ray diffraction analysis, and supported by EHMO and ab initio analyses, indica…

Molecular structures and vibrations of m-methylaniline in the S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calcu…

2000

Abstract The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled m-methylaniline have been obtained for the S1←S0 transition, in which some of the bands have been observed for the first time. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes. It was found that the spectra exhibit an important feature which is the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31G* and CIS/6-31G* show that the optimized structure of m-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence…