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

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