Small gold species at hydroxylated alumina surfaces. A computational study using embedded-cluster models of alpha-Al2O3(0001)

We calculated equilibrium structures for adsorption complexes of gold monomers, dimers, and trimers on a alpha-Al2O3(0001) model surface, partially covered by mu(1) and mu(3) hydroxyl groups. We applied a scalar-relativistic gradient-corrected density functional method to cluster models of the support that were embedded in an elastic polarizable environment. The most stable structures, with calculated adsorption energies in the range 0.81-1.74 eV, feature coordination bonds to surface mu(1)-OH group and are 0.24-0.79 eV more stable than the corresponding Au-n complexes on a dehydrated surface. Isomeric rearrangements of the most stable complexes are hindered by barriers of 0.65-1.08 eV. (C) 2010 Elsevier B. V. All rights reserved

Small gold species supported on alumina. A computational study of alpha-Al2O3(0001) and gamma-Al2O3(001) using an embedded-cluster approach

We calculated the structures of and analyzed the bonding in adsorption complexes of small gold species Au-n on alpha-Al2O3(0001

Trinuclear tantalum clusters grafted to hydroxylated silica surfaces: A density-functional embedded-cluster study

To identify the coordination modes of bare and hydrogenated trinuclear tantalum species on hydroxylated silica, we computationally examined models of Ta3H (n)

Density functional embedded cluster calculations on Lewis acid centers of the α-Al₂O₃(0001) surface: Adsorption of a CO probe

We have investigated the adsorption of CO on the cation-terminated (0001) surface of -Al2O3 with a generalized-gradient density functional approach. We used cluster models that are consistently embedded in an elastic polarizable environment (EPE), employing a (classical) shell model scheme and bare pseudopotentials (Alpp*) for cations at the cluster boundary. The newly implemented EPE method was found to perform well for describing structure and adsorption properties of Lewis acidic centers of the polar (0001) surface known for its strong relaxation with respect to the bulk terminated geometry. The calculated data are stable with respect to the size of the cluster models. For the embedded stoichiometric clusters [Al4O6]/Al and [Al10O15]/Al of different structure, the adsorption induced shift of the CO stretching vibration and the binding energy (BE) are 30-42 cm-1 and 0.38-0.47 eV, respectively. The results for the frequency shifts are in good agreement with the value of 39 cm-1 measured for CO/-Al2O3(0001) at low coverages. Judged by the frequency shift and the adsorption energy, the interaction of CO molecules with three-coordinated Al3+ cations at the regular surface is very similar to that with Mg2+ corner sites of MgO polycrystallites, =39 cm-1, BE=0.38 eV. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 200

Layered structure of the near surface region of oxidized chalcopyrite CuFeS2 hard X ray photoelectron spectroscopy, X ray absorption spectroscopy and DFT U studies

Metal-depleted layers with different S species are found, and mechanisms for their formation and metal sulfide ‘passivation’ are proposed.</p

Density-functional model cluster studies of EPR g tensors of F-s(+) centers on the surface of MgO

We report g tensors of surface color centers, so-called F-s(+) centers, of MgO calculated with two density-functional approaches using accurately embedded cluster models. In line with recent UHV measurements on single-crystalline MgO film, we determined only small g-tensor anisotropies and negative shifts Delta g equivalent to g-g(e) for all F-s(+) sites considered, namely, (001)-terrace, step, edge, and corner sites. The g values are very sensitive to the local structure of the defect: relaxation reverses the sign of Delta g. However, accounting for the spin-orbit interaction either self-consistently or perturbatively yields very similar results. In addition to the values of the tensor components, their direction with respect to the surface was determined. In contrast to edges, significant deviations from ideal C-2v symmetry were found for F-s(+) centers at steps. Recent data on single-crystalline thin films are reevaluated in the light of these results

The Computational Study of Small Gold Species Adsorbed on Hydroxylated Alumina Surfaces

Рассчитаны равновесные структуры адсорбционных комплексов мономеров, димеров и тримеров золота на поверхности -Al2O3 (0001), содержащей 1- и 3-гидроксильные группы. Для расчета кластерных моделей подложки, внедренных в эластичное поляризуемое окружение, применялся скалярно-релятивистский метод функционала плотности с коррекцией градиента. Наиболее устойчивые структуры с энергиями адсорбции, рассчитанными в диапазоне 0,81-1,74 эВ, характеризуются координационными связями с поверхностными 1- ОН-группами, являясь на 0,24-0,79 эВ более стабильными, чем соответствующие комплексы Aun на дегидроксилированной поверхности.We calculated equilibrium structures for adsorption complexes of gold monomers, dimers, and trimers on a -Al2O3(0001) model surface, partially covered by 1 and 3 hydroxyl groups. We applied a scalar-relativistic gradient-corrected density functional method to cluster models of the support that were embedded in an elastic polarizable environment. The most stable structures, with calculated adsorption energies in the range 0.81-1.74 eV, feature coordination bonds to surface 1-OH group and are 0.24-0.79 eV more stable than the corresponding Aun complexes on a dehydrated surface. Isomeric rearrangements of the most stable complexes are hindered by barriers of 0.65-1.08 eV

The Computational Study of Small Gold Species Adsorbed on Hydroxylated Alumina Surfaces

Рассчитаны равновесные структуры адсорбционных комплексов мономеров, димеров и тримеров золота на поверхности -Al2O3 (0001), содержащей 1- и 3-гидроксильные группы. Для расчета кластерных моделей подложки, внедренных в эластичное поляризуемое окружение, применялся скалярно-релятивистский метод функционала плотности с коррекцией градиента. Наиболее устойчивые структуры с энергиями адсорбции, рассчитанными в диапазоне 0,81-1,74 эВ, характеризуются координационными связями с поверхностными 1- ОН-группами, являясь на 0,24-0,79 эВ более стабильными, чем соответствующие комплексы Aun на дегидроксилированной поверхности.We calculated equilibrium structures for adsorption complexes of gold monomers, dimers, and trimers on a -Al2O3(0001) model surface, partially covered by 1 and 3 hydroxyl groups. We applied a scalar-relativistic gradient-corrected density functional method to cluster models of the support that were embedded in an elastic polarizable environment. The most stable structures, with calculated adsorption energies in the range 0.81-1.74 eV, feature coordination bonds to surface 1-OH group and are 0.24-0.79 eV more stable than the corresponding Aun complexes on a dehydrated surface. Isomeric rearrangements of the most stable complexes are hindered by barriers of 0.65-1.08 eV