Search results for "Bond"
showing 10 items of 3527 documents
Size-consistent ab initio calculation of the electric quadrupole moment of Cl2
2003
Abstract The molecular electric quadrupole moment ( Θ ) of Cl 2 has been calculated using SDCI, and (SC) 2 -SDCI wave functions as well as CCSD, CCSD(T), and CC3 methods. All these correlation methods are single reference. All of them, but SDCI, are free of the size-extensivity error. The variation of Θ from the separated atoms to the equilibrium region is reported. The present results leads to an estimated value of 2.3520 a.u. (10.55 × 10 −40 Cm 2 ) corresponding to a CC(3) calculation at the CBS approach and including the ro-vibrational and thermal averaging corrections. This value is compatible with two experimental values and points to one of them as slightly more reliable.
Semi-Empirical Calculations of Hole Polarons in MgO and KNbO3 Crystals
1998
The semi-empirical quantum chemical INDO method has been used for cluster and large unit cell calculations of hole polarons bound to a cation vacancy in highly ionic MgO and partly covalent perovskite KNbO 3 . In both cases a hole is well localized on an oxygen atom displaced towards the vacancy. The calculated optical and thermal ionization energies for V - and V 0 centers are in excellent agreement with experimental data for MgO. In KNbO 3 we predict the existence of one-site and two-site (molecular) polarons with close absorption energies (1 e V). The relevant experimental data are discussed.
Modeling of defects and surfaces in perovskite ferroelectrics
2002
The results of electronic structure calculations for different terminations of SrTiO3 (100) and (110) perovskite thin films are discussed. These calculations are based on the ab initio Hartree-Fock (HF) method and Density Functional Theory (DFT). Results are compared with previous ab initio plane-wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti – O chemical bond covalency nearby the surface is confirmed by experimental data. Our quantum chemical calculations performed by means of the intermediate neglect of differential overlap (INDO) method confirm the existence of self-trapped electrons in KNbO3, KTaO3 and BaTiO3 crystals. The relevant latti…
Coupling between bulk- and surface chemistry in suspensions of charged colloids
2013
The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular weight microions, and colloidal macroions with acidic surface groups, from a self-consistent solution of a coupled physicochemical set of nonlinear algebraic equations and non-mean-field liquid integral equations. Here, we study suspensions of colloidal spheres with sulfonate or silanol surface groups, suspended in demineralized water that is saturated with carbon dioxide under standard atmosphere. The only input required for our theoretical…
The Coordination of Uranyl in Water: A Combined Quantum Chemical and Molecular Simulation Study
2005
The coordination environment of uranyl in water has been studied using a combined quantum mechanical and molecular dynamics approach. Multiconfigurational wave function calculations have been performed to generate pair potentials between uranyl and water. The quantum chemically determined energies have been used to fit parameters in a polarizable force field with an added charge transfer term. Molecular dynamics simulations have been performed for the uranyl ion and up to 400 water molecules. The results show a uranyl ion with five water molecules coordinated in the equatorial plane. The U-O(H(2)O) distance is 2.40 A, which is close to the experimental estimates. A second coordination shell…
<title>Ion and electron trapping: release and relaxation processes in fluoride crystals</title>
2001
The thermally stimulated relaxation (TSR) processes in CaF2, BaF2 and LiBaF3 crystals (X-ray irradiated at LNT or RT) have been investigated by means of the ionic conductivity, thermally stimulated (TS) ionic depolarization current (TSDC), TS current (TSC), TS luminescence (TSL) and thermal bleaching techniques. The ionic TSDC measurements evidence that under DC field fluorides accumulate large ionic space-charge (thermoelectric state is formed) as a result of the migrating anion interstitial and/or vacancy capture on defects. In the ionic conductivity region (290 - 650 K) the thermoelectric state anneals, and several wide and overlapping anionic TSDC peaks are detected. The ionic TSDC stag…
Hybrid layers of etch-and-rinse versus self-etching adhesive systems.
2010
Objective: To evaluate the effectiveness in the formation of resin tags, adhesive lateral branches and hybrid layers of five adhesive systems, when bonding to dentine. Material and Methods: Flat dentin surfaces from 25 molars were bonded with several adhesive systems according to the manufacturers? instructions. Composite build-ups were constructed incrementally with Tetric Ceram. The Specimens were sectioned parallel to the long axis. One section was treated with phosphoric acid and sodium hypochlorite in order to reveal the hybrid layer formation. The other section was stored in 30% hydrochloric acid to detect resin tags and adhesive lateral branch formation. Results: The two etch-and-rin…
Molecular balance forms of indium phthalocyanines in benzene and pyridine solution
2019
Abstract The electronic absorption spectra of In2Pc3, InPc2 and InPcI solid compounds after dissolvation in one of the most commonly used solvents, i.e.: benzene and pyridine have been measured. In benzene, the molecules of the diindium tripledecker phthalocyanine, In2Pc3, undergoes transformation to ionic couples [InPc]+[InPc2]-, whereas when the InPc2 compound is dissolvated, the molecules of the indium sandwiches, InPc2, remain relatively stable in the solvent. When the In2Pc3 compound is dissolvated in py, the inner Pc(2-) ring of diindium tripledecker phthalocyanine molecule undergoes disjunction and rejection. In the results of it in the solution the couple of chromophores, being in t…
Theoretical Study of the Electronic Excited States of Tetracyanoethylene and Its Radical Anion
2005
The low-lying electronic states of tetracyanoethylene (TCNE) and its radical anion were studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The results obtained yield a full interpretation of the electronic absorption spectra, explain the spectral changes undergone upon reduction, give support to the occurrence of a bound excited state for the anionic species, and provide valuable information for the rationalization of the experimental data obtained with electron transmission spectroscopy.
Investigation of molecular dimers by ensemble and single molecule spectroscopy
2002
International audience; We have investigated molecular dimers with different electronic coupling strengths by bulk and single molecule spectroscopy. In one of the dimers the two monomers (perylene-monoimide) are directly connected via a single bond while in the other one they are separated by the benzil motif. The close proximity of the monomers in the first case gives rise to excitonic band splitting which is clearly observable in the bulk absorption spectra. For the benzil structure the electronic interactions are governed by Förster-type energy hopping between the monomers. Fluorescence intensity trajectories at the single molecule level show one-step and two-step bleaching behaviour whi…