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Wyszukujesz frazę "Pietrzyk, Piotr" wg kryterium: Wszystkie pola


Tytuł:
Paramagnetic species on catalytic surfaces : DFT investigations into structure sensitivity of the hyperfine coupling constants
Autorzy:
Sojka, Zbigniew
Pietrzyk, Piotr
Opis:
Structure sensitivity of the hyperfine coupling constants was investigated by means of DFT calculations for selected surface paramagnetic species. $A\cdot CH_{2}OH$ radical trapped on silica and intrazeolite copper nitrosyl adducts encaged in ZSM-5 were taken as the examples. The surface of amorphous silica was modeled with a $[Si_{5}O_{8}H_{10}]$ cluster, whereas the zeolite hosting sites were epitomized by $[Si_{4}S=AlO_{5}(OH)_{10}]^{-}$ cluster. Three different coordination modes of the $\cdot CH_{2}OH$ radical were considered and the isotropic $^{13}\textrm{C}$ and $^{1}\textrm{H}$ hyperfine constants of the resultant van der Waals complexes, calculated with B3LYP/6-311G(d), were discussed in terms of the angular deformations caused by hydrogen bonds with the cluster. The magnetic parameters of the $\eta^{1}-N(CuNO)^{11}$ and $\eta^{1}-O(CuNO)^{11}$ linkage isomers were calculated at the BPW91/LanL2DZ and 6-311G(df) level. For the most stable $\eta^{1}-N$ adduct a clear dependence of the spin density distribution within the Cu-NO moiety on changes in the Cu-N-O angle and the Cu-N bond distance was observed and accounted for by varying spin polarization and delocalization.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Magnetic properties of monomer and dimer tetrahedral VO_x entities dispersed on amorphous silica-based materials : prediction of EPR parameters from relativistic DFT calculations and broken symmetry approach to exchange couplings
Autorzy:
Sojka, Zbigniew
Pietrzyk, Piotr
Opis:
Molecular structures of the isolated tetrahedral oxovanadium(IV) and bridged $\mu$-oxo-divanadium(IV) complexes hosted by the clusters mimicking surfaces of amorphous silica-based materials were investigated using density functional theory (DFT) calculations. Principal values of the g and A tensors for the monomer vanadyl species were obtained using the coupled-perturbed DFT level of theory and the spin--orbit mean-field approximation (SOMF). Magnetic exchange interaction for the \mu-oxo bridged vanadium(IV) dimer was investigated within the broken symmetry approach. An antiferromagnetic coupling of the individual magnetic moments of the vanadium(IV) centers in the [VO-O-VO]2+ bridges was revealed and discussed in detail. The coupling explains pronounced decrease of the electron paramagnetic resonance signal (EPR) intensity, observed for the reduced VOx/SiO2 samples with the increasing coverage of vanadia, in terms of transformation of the paramagnetic monomer species into the dimers with S = 0 ground state.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł

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