H Atom Adsorption on a Silicate Surface: The (010) Surface of Forsterite

Abstract

We present a first-principles computational study of the interaction of an H atom with the (010) surface of forsterite (Mg 2 SiO 4 ). Periodic DFT-GGA calculations (PBE) are carried out using the SIESTA code with core pseudopotentials and TZP localized basis sets. Potential energy curves are determined for the approach of the H atom toward different sites of the surface: atop, near, or in between the O, Mg, and Si atoms. An outer adsorption well is found for all investigated sites; it is deepest (162 meV) at a so-called "displaced Mg− O bridge" position. The binding at this well is of the "weak chemisorption"/"strong physisorption" type. An inner stronger chemisorption well (670 meV deep) exists exclusively near an O site but not strictly atop. Depending on the path, we find activation barriers (25− 170 meV high) against chemisorption, the lowest of these occurs for the top O site. General trends of the computed interaction energies qualitatively agree with the QM/MM results of Goumans et al. [Mon. Not. R. Astron. Soc. 2009, 393, 1403, but adsorption binding energies and barrier heights differ significantly.

Interstellar H adsorption and H2formation on the crystalline (010) forsterite surface: a B3LYP-D2* periodic study

“…This is somehow at variance with the work by Sidis et al 19 in which H was predicted to remain attached to a second less exposed oxygen atom as well as with the results by Downing et al, 20 in which H was predicted to chemisorb also at the surface Mg ion. Nevertheless, for both cases the adsorption was much less favorable than for the cases also (and only) found in the present work.…”

Relevance of silicate surface morphology in interstellar H2formation. Insights from quantum chemical calculations

“…Quantum dynamics studies addressed the H 2 formation on coronene clusters and C(0001) surfaces as models of carbonaceous dust grains (Meijer, Fisher & Clary 2003;Morisset et al 2005;Bachellerie et al 2009;Rougeau, Teillet-Billy & Sidis 2011;Casolo, Tantardini & Martinazzo 2013). By means of periodic calculations, the H adsorption on the (010) crystalline Mg 2 SiO 4 and Fe 2 SiO 4 surfaces (Downing et al 2013;Garcia-Gil et al 2013;Navarro-Ruiz et al 2014) were exhaustively explored, showing neighbour Mg and O ions as the most favourable sites for physisorption and chemisorption, respectively. Similar results were obtained by Goumans et al (Goumans & Bromley 2011) for the H adsorption on a ultra-small Mg 4 Si 4 O 12 silicate cluster (less than 15 Å in diameter).…”

First‐principle modelling of forsterite surface properties: Accuracy of methods and basis sets

“…In recent years, a number of papers have appeared, tackling the complex task of developing models able to provide a reliable description of the atomic details of this mineral interface . Most of these studies focus on the interaction of hydrogen, water, or carbon dioxide with the (010) surface of forsterite (where both M sites are occupied by magnesium) as modeled either with interatomic potentials, or with first‐principle methods based on the density functional theory (DFT) .…”

“…Most of these studies focus on the interaction of hydrogen, water, or carbon dioxide with the (010) surface of forsterite (where both M sites are occupied by magnesium) as modeled either with interatomic potentials, or with first‐principle methods based on the density functional theory (DFT) . Of the latter, one presents a study on the adsorption of H 2 molecules on the (010) surface of forsterite performed at the hybrid meta‐generalized gradient approximation (GGA) level of theory, though structures were optimized using interatomic potentials; four deal with the adsorption of either water molecules or H atoms and H 2 molecules on the same surface, simulated at the GGA and B3LYP‐D* levels. Very recently, a GGA study on the adsorption of water molecule on the (100) surface has also been published …”