Search results for "Orbital"
showing 10 items of 679 documents
3-Vinyl-1H-indoles: A conformational study, electronic aspects and reactivity predictions forDiels-Alder reactions
1995
On the basis of X-ray geometries, a theoretical conformational study of some 3-vinyl-1H-indoles was performed with quantum chemistry and molecular mechanics programs. Charge, frontier orbitals, and the molecular electrostatic potential derived from quantum chemistry calculations of 3-vinyl-1H-indoles are reliable reactivity parameters to predict the outcome of theDiels-Alder reaction.
Meaning and magnitude of the reduced density matrix cumulants
2012
Abstract Within the framework of a generalized normal ordering (GNO), invented by Mukherjee [1] , the reduced density matrix cumulants of the (multiconfigurational) reference wave function play a central role, as they arise directly from the contraction rules. The extended Wick theorem allows contractions of an arbitrary number of active annihilators and creators through a cumulant of corresponding rank. Because the cumulant rank truncates naturally only at the number of active spin orbitals, practical applications of the GNO concept seem to rely on a fast convergence of the cumulant series, allowing one to neglect cumulants with high rank. By computing cumulant norms for selected systems (…
Ab initio study of the C60+Na system
2004
Abstract In this work we present the first CAS-CI calculation of the potential-electronic curves for the lowest states of the C 60 +Na system using a set of local orbitals. These orbitals permit to select a small active space describing the ionic interaction between the C 60 and the Na atom. A binding energy of about 3 eV has been found, a value substantially larger than previous theoretical results.
The characterization of molecular alkaly metal azides
2006
Matrix isolation infrared (IR) studies have been carried out on the vaporisation of the alkali-metal azides MN(3) (M = Na, K, Rb and Cs). The results show that under high vacuum conditions, molecular KN(3), RbN(3) and CsN(3) are present as stable high-temperature vapour species, together with variable amounts of nitrogen gas and the corresponding metal atoms. The characterisation of these molecular azides is supported by ab initio molecular orbital calculations and density functional theory (DFT) calculations, and for CsN(3) in particular, by the detection of the isotopomers CS((14)N(15)N(14)N) and Cs((15)N(14)N(14)N). The IR spectra are assigned to a "side-on" (C(2v)) structure by comparis…
Structural and electronic properties of β-NaYF4 and β-NaYF4:Ce3+
2020
AP is indebted for a financial support provided by Scientific Research Project grant for Students and Young Researchers Nr. SJZ/2017/3 sponsored at the Institute of Solid State Physics, University of Latvia , while AIP is thankful for the financial support from Latvian Research Council lzp-2018/1-0214 .
Comparative analysis of the electronic structures of mono- and bi-atomic chains of IV, III–V and II–VI group elements calculated using the DFT LCAO a…
2015
Using the first principle non-relativistic linear combination of atomic orbitals (LCAO) and relativistic linearized augmented cylindrical wave (LACW) methods, the band structure of the covalent and partially ionic ANB8−N single atom width chain is calculated. Both the LCAO and LACW methods show that the chains of C, Si, Ge, Sn, and Pb are metallic. However, there is a great difference between the relativistic and non-relativistic band structures. The π bands crossing the Fermi level are orbitally doubly degenerate in the non-relativistic model. The relativistic LACW calculations demonstrate that the spin and orbital motion of electrons are coupled, thereby splitting the π bands. The spin–or…
Cation Environment in BaCeO3-Based Protonic Conductors: a Computational Study
2009
Geometry calculations were performed on pure BaCeO(3) fragments and on Y- and In-doped derivatives. HF and DFT approaches were used to investigate monoclinic and orthorhombic structures. The computational methods, structural models, and electronic structure investigation protocols were tuned taking into consideration and balancing the consistency of the results against the computational cost. The calculated structures and energetics parameter, as well as the detailed orbital analysis performed on the corresponding BaCeO(3) derivatives allowed us to explain experimental findings and to develop a procedure to study the cationic octahedral environment of doped X:BaCeO(3) (X = Y, In) and undope…
Theoretical study of stationary structures of acetamidine unimolecular decomposition
1990
Abstract The unimolecular decomposition of acetamidine to ammonia and acetonitrile was examined by ab initio methods. Stationary points, i.e. the reactant, product and transition structures, have been characterized. The process has an asynchronous mechanism, the transition state being described as a four-membered ring. To establish the relevance of different basis sets, calculations with eight standard Gaussian basis sets, STO-3G, 3-21G, 4-21G, 4-31G, 6-31G, 6-311G, 6-31G*, and G-31G**, were carried out.
1,3-Dipolar cycloadditions of electrophilically activated benzonitrile N-oxides. Polar cycloaddition versus oxime formation.
2006
The reactions of electrophilically activated benzonitrile N-oxides (BNOs) toward 3-methylenephthalimidines (MPIs) have been studied using density functional theory (DFT) at the B3LYP/6-31G* level. For these reactions, two different channels allowing the formation of the [3 + 2] cycloadducts and two isomeric (E)- and (Z)-oximes have been characterized. The 1,3-dipolar cycloadditions take place along concerted but highly asynchronous transition states, while formation of the oximes is achieved through a stepwise mechanism involving zwitterionic intermediates. Both reactions are initiated by the nucleophilic attack of the methylene carbon of the MPIs to the carbon atom of the electrophilically…
On the mechanism of catalytic isomerization of xylenes. Molecular orbital studies
1979
Abstract On the basis of CNDO/2 molecular orbital calculations, we postulate the following detailed mechanism for the catalytic isomerization of xylenes which explains the initial product distributions and also our previous finding that the reaction is intramolecular: (i) adsorption of xylene on a surface acid site to form a Wheland-type complex; (ii) disrotatory cyclization of the protonated species into a bicyclo[3, 1, 0]hexenyl complex; (iii) migration of the methylene bridge to a new side of the pentagonal ring; (iv) change of the new bicyclic species back into the corresponding Wheland-type complex; (v) desorption of the xylene isomer from the surface of the catalyst. The overall rate …