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Density functional theory (DFT) calculations combined with surface thermodynamic arguments and the Gibbs-Curie-Wulff equilibrium morphology formalism have been employed to explore the effect of the reaction conditions, temperature (T), and gas-phase partial pressures (p H 2 and p H 2 S ) on the stability of low Miller index ruthenium sulfide (RuS 2 ) surfaces. The calculated thermodynamic surface stabilities and the resulting equilibrium morphology models suggest that unsupported RuS 2 nanoparticles in HDS conditions are like to a polyhedron with six, eight, and twelve (100), (111), and (102) faces, respectively. The area of these faces covers about 40%, 37%, and 23% of the total particle, respectively. The atomic basins of the outermost individual atoms of the exposed surfaces were determined using the quantum theory of atoms in molecules methodology. Direct visualization of these basins has shown that a hole just at the middle of the outermost sulfur basins provides access to uncovered metal sites. Analysis of the electrostatic potential mapped onto a selected electron density isocontour (0.001 au) on the exposed surface reveals a very high potential reactivity of these holes toward electrodonating reagents. Consequently, the high attraction between these uncovered sites and S atoms coming from reagent polluting molecules makes these kinds of particles quite active for HDS catalysis.

The nonframework cation sites for K-ETS-10 and Na-ETS-10 have been modeled using molecular simulation techniques. This work combines a Monte Carlo packing procedure with lattice energy calculations, to simulate the charge-balancing cation sites in a titanosilicate, starting from only the framework structural data. One hundred trial packing arrangements for each cation type were randomly generated with the Monte Carlo procedure, and the lattice energy for each of these structures was calculated, considering electrostatic and repulsive short-range terms. For both K+ and Na+ cations, most of the initial arrangements converged to an identical minimum energy structure, involving four different cation sites. The relative stability of these sites depends on their framework environment and the kind of cation that occupies them.

The atomic layer deposition (ALD) of aluminum oxide (Al 2 O 3 ) from trimethylaluminium and water on silicon nitride was studied on as-received and HF-cleaned Si 3 N 4 surfaces. In situ spectroscopic ellipsometry during ALD, X-ray photoelectron spectroscopy, X-ray reflectivity, and time-of-flight secondary ion mass spectrometry were used to elucidate the growth rate, the chemical composition, and the density of Al 2 O 3 . The effect of the substrate cleaning and of the growth temperature -varied in the 150−300 °C rangewere analyzed by considering first-principles calculations of the early stages of the growth on both Si 3 N 4 and SiO 2 surfaces. Our work evidenced how not only complete ALD cycles but also complementary non-ALD reactions can account for the observed peculiarities related to the enhanced or inhibited growth rates on the Si 3 N 4 surfaces as a function of temperature.