Search results for " Quantum chemistry"
showing 10 items of 549 documents
Dissociation mechanisms of cluster ions resolved using ab-initio molecular orbital calculations
2007
We have examined the cluster-size effect on fragments in the collision-induced dissociation (CID) of small boron clusters (B + n , n ≤ 8) by means of ab-initio molecular orbital (MO) calculation, for conditions representative of low-Z cationic clusters in plasma. Single cations B + (leaving B 0 n-1 ) are predominantly fragmented from small clusters B + n (n < 5) by low-energy collisions (<10 eV) with Xe atoms. With increasing the size n, beyond n = 5, B + n-1 (leaving B°) clusters are observed preferentially. This alternating trend in experiment has not been quantitatively explained by previous ab-initio MO calculations. We used a density functional method called B3LYP and basis functions 6…
Comparative ab initio calculations of SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) heterostructures
2016
Abstract Using a B3PW hybrid exchange–correlation functional within the density functional theory (DFT) we calculated from the first principles the electronic structure of BaTiO 3 /SrTiO 3 and PbZrO 3 /SrZrO 3 (0 0 1) interfaces. The optical band gap of both BaTiO 3 /SrTiO 3 and PbZrO 3 /SrZrO 3 (0 0 1) interfaces depends mostly from BaO or TiO 2 and SrO or ZrO 2 termination of the upper layer, respectively. Based on the results of our calculations we predict increase of the Ti–O and Zr–O chemical bond covalency near the SrTiO 3 /BaTiO 3 and SrZrO 3 /PbZrO 3 (0 0 1) interfaces as compared to the BaTiO 3 and PbZrO 3 bulk.
Comparative quantum chemistry study of the F-center in lanthanum trifluoride
2020
Abstract In this study we report the results of first principle quantum chemical modeling of electronic structure and spatial configuration of LaF3 crystal containing the F-center. Theoretical predictions of atomic and electronic properties of LaF3 are given by means of density functional theory. From our modeling we predict that the F-center placed at fluorine ion position between the lanthanum planes at tysonite LaF3 is the most energetically stable. In order to interpret the structure of the optical absorption spectrum of X-irradiated LaF3 we performed calculations of excited and transition states of the F-center within the embedded cluster formalism using time dependent density function…
Radiation effects on silica-based preforms and optical fibers-II: Coupling ab initio simulations and experiments
2008
International audience; Abstract—Experimental characterization through electron paramagnetic resonance (EPR) and confocal luminescence microscopy (CML) of a Ge-doped glass (preform and fiber) reveals the generation of several point defects by 10 keV X-ray radiation-induced attenuation: GeE', Ge(1), Ge(2), and Ge-ODC. The generation mechanisms of Ge-ODC and charged defects like GeE' centers are studied through ab initio simulation. Our calculations used a 108 atom supercell with a glass composition comparable to the Ge-doped core or to the pure-silica cladding of the canonical sample. The large size of our cell allows us to study the influence of the local environment surrounding the X-ODC d…
Trapping of hydrogen and helium at dislocations in tungsten: anab initiostudy
2017
Retention of plasma gas components such as hydrogen (H) isotopes and helium (He) is one of the limiting factors in selection of plasma facing materials for future thermonuclear fusion devices. Tungsten (W) is one of the promising candidates for such materials and was chosen for the divertor armor for International Thermonuclear Experimental Reactor (ITER) and the first wall material for the design of the demonstrational fusion power plant - DEMO. For the analytical estimation of accumulation of H/He components in tungsten, it is important to understand the relevant physical mechanisms of their trapping in the material and thoroughly parameterize them numerically. Experiments involving high …
Model nuclear energy density functionals derived from ab initio calculations
2020
We present the first application of a new approach, proposed in [Journal of Physics G: Nuclear and Particle Physics, 43, 04LT01 (2016)] to derive coupling constants of the Skyrme energy density functional (EDF) from ab initio Hamiltonian. By perturbing the ab initio Hamiltonian with several functional generators defining the Skyrme EDF, we create a set of metadata that is then used to constrain the coupling constants of the functional. We use statistical analysis to obtain such an ab initio-equivalent Skyrme EDF. We find that the resulting functional describes properties of atomic nuclei and infinite nuclear matter quite poorly. This may point out to the necessity of building up the ab init…
Ab initio modelling of the initial stages of the ODS particle formation process
2018
Abstract Oxide-Dispersion Strengthened (ODS) steels with Y2O3 nanoparticles are promising structural materials for fision and future fusion reactors. A large number of experimental as well as theoretical studies provided valuable information on the ODS particle formation process. However, some important details of this process still remain unexplained. We present the results of ab initio VASP calculations of the initial steps of the ODS particle formation. At these steps Y solute atoms are stabilized in the Fe lattice by vacancies, which create a basis for the future growth of Y2O3-particle. Interaction of multiple vacancies and solution Y and O atoms has been studied in various combination…
Relativistic effects and spin observables in deuteron electrodisintegration
1993
The influence of relativistic effects in deuteron electrodisintegration, in particular their manifestation in spin observables, is discussed. We have used a simple phenomenological approach by adding the lowest-order relativistic corrections to the nonrelativistic one-body current and including the kinematic wave-function boost. Furthermore, final-state interaction, meson-exchange currents and isobar configurations are included in order to study kinematic regions off the quasi-free case. Sizeable relativistic effects in many observables are found even at low energies.
The impact of the properties of the heaviest elements on the chemical and physical sciences
2012
Abstract The unique role of the heaviest elements in chemical and physical sciences is discussed. With the actinide series (Z = 90-103) and the superactinide series (Z = 122-155), the heaviest elements have significantly shaped the architecture of the Periodic Table of the elements. Relativistic effects in the electron shells of the heaviest elements change the chemical properties in a given group in a non-linear fashion. Relativistically stabilized sub-shell closures give rise to a new category of elements in the Periodic Table: volatile metals. The prototype for this property is element 114 which, due to the relativistic stabilization of its 7s2 7p2 1/2 electron configuration, is volatile…
H−ZSM-5 Modified Zeolite: Quantum Chemical Models of Acidic Sites
2007
A ZSM-5 fragment, containing 52 tetrahedral moieties, each of them formed by one silicon or one aluminum atom surrounded by four oxygen atoms, was employed to model (52T systems) by quantum chemical calculations (i) the influence of the positions of the acidic sites on the energetics of 22 aluminum monosubstituted and bisubstituted 52T acidic zeolite (H-ZSM-5) systems and (ii) the local adsorption properties and acidic strength of the corresponding -OH sites. The energetics and the structural properties of simpler acid H-ZSM-5 systems containing only five Tetrahedral moieties (5T systems) were also modeled for comparison. B3LYP/6-31G(d,p) partial geometry optimization routines were performe…