QuantumATK: an integrated platform of electronic and atomic-scale modelling tools.

QuantumATK is an integrated set of atomic-scale modelling tools developed since 2003 by professional software engineers in collaboration with academic researchers. While different aspects and individual modules of the platform have been previously presented, the purpose of this paper is to give a general overview of the platform. The QuantumATK simulation engines enable electronic-structure calculations using density functional theory or tight-binding model Hamiltonians, and also offers bonded or reactive empirical force fields in many different parametrizations.

Unravelling Site-Specific Photo-Reactions of Ethanol on Rutile TiO2(110).

Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding and the development of efficient catalytic systems. Here we have studied the photo-activated dehydrogenation of ethanol on reduced and oxidized rutile TiO2(110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques and theoretical calculations we found that the photo-reaction proceeds most efficiently when the reactants are adsorbed on regular Ti surface sites, whereas species that are strongly adsorbed at surface defects such as O vacancies and step edges show little reaction under reducing conditions.

Effect of Sb Segregation on Conductance and Catalytic Activity at Pt/Sb-Doped SnO2 Interface: A Synergetic Computational and Experimental Study.

Antimony-doped tin dioxide (ATO) is considered a promising support material for Pt-based fuel cell cathodes, displaying enhanced stability over carbon-based supports. In this work, the effect of Sb segregation on the conductance and catalytic activity at Pt/ATO interface was investigated through a combined computational and experimental study. It was found that Sb-dopant atoms prefer to segregate toward the ATO/Pt interface.

A density functional theory study of atomic steps on stoichiometric rutile TiO2(110).

We present a detailed theoretical study of the energetics of stoichiometric steps on the (110) surface of rutile TiO2. Step structures running along the <001>, <111>, and <110> directions including bulk-terminations and possible reconstructions have been considered. A robust method for extracting surface and step energies of vicinal surfaces, where the surface energies converge slowly with respect to slab thickness, is outlined and used.

Ethanol Diffusion on Rutile TiO2(110) Mediated by H Adatoms.

We have studied the diffusion of ethanol on rutile TiO2(110)-(1 × 1) by high-resolution scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Time-lapsed STM images recorded at ∼200 K revealed the diffusion of ethanol molecules both parallel and perpendicular to the rows of surface Ti atoms. The diffusion of ethanol molecules perpendicular to the rows of surface Ti atoms was found to be mediated by H adatoms in the rows of bridge-bonded O (Obr) atoms similarly to previous results obtained for water monomers.

Adsorption properties versus oxidation states of rutile TiO2(110).

Using density functional theory we have studied the adsorption properties of different atoms and molecules deposited on a stoichiometric, reduced, and oxidized rutile TiO(2)(110) surface. Depending on the oxidation state of the surface, electrons can flow from or to the substrate and, therefore, negatively or positively charged species are expected. In particular, we have found that a charge transfer process from or to the surface always occurs for highly electronegative or highly electropositive species, respectively.

Direct measurement of the attractive interaction forces on F0 color centers on MgO(001) by dynamic force microscopy.

Defect sites on oxide surfaces play a dominant role in surface chemistry. The direct atomistic study of these sites is important but very difficult. We have mimicked the adsorbate-defect interaction by a dynamic force microscope tip measuring the interaction with a color center (F(0)) on the MgO(001) surface.

Stabilizing monomeric iron species in a porous silica/Mo(112) film.

The stabilization of single Fe atoms in the nanopores of an ultrathin silica film grown on Mo(112) is demonstrated with scanning tunneling microscopy (STM) and density functional theory (DFT). The Fe atoms are able to penetrate the openings in the oxide surface and adsorb in two different binding configurations at the metal-oxide interface. In the energetically preferred site, the Fe stays monomeric even at temperatures above 300 K.

Mechanism of charging of Au atoms and nanoclusters on Li doped SiO2/Mo(112) films.

We present the results of supercell DFT calculations on the adsorption properties of Au atoms and small clusters (Au(n), n < or = 5) on a SiO(2)/Mo(112) thin film and on the same system modified by doping with Li atoms. The adsorbed Li atoms penetrate into the pores of the silica film and become stabilized at the interface where they donate one electron to the Mo metal. As a consequence, the work function of the Li-doped SiO(2)/Mo(112) film is reduced and results in modified adsorption properties.

Tailoring the interaction strength between gold particles and silica thin films via work function control.

The possibility to modify the adsorption properties of a porous silica/Mo(112) film by controlling its work function has been studied by a combined STM and density-functional theory approach. While the original film is inert towards metal adsorption, Au atoms and clusters can be stabilized on the surface after Li doping. The Li atoms penetrate the topmost silica layer and bind as Li+ cations at the metal-oxide interface, thereby reducing the oxide work function.

Enhanced magnetic moments of Fe clusters supported on MgO/Fe(001) ultrathin films.

We report on the unusual behavior of Fe(n) clusters (n < or = 6) supported on ultrathin oxide films. When the film is grown on a Mo(001) support, the cluster magnetic moments exhibit a similar quenching as on the bare MgO(001) surface while on MgO/Fe(001) films the magnetization is enhanced due to a charge transfer from the Fe clusters to the MgO/Fe(001) interface. These results obtained using a spin-polarized density functional approach show the potential of using ultrathin films to tune the properties of supported magnetic particles.

Modifying the adsorption characteristic of inert silica films by inserting anchoring sites.

The adsorption properties of thin silica films on Mo(112) have been tailored by embedding single Pd atoms into the nanopores of the oxide material. The embedded Pd is able to anchor metal adatoms that would not bind to the inert silica surface otherwise. Several adsorption structures, e.

Tuning the work function of ultrathin oxide films on metals by adsorption of alkali atoms.

We report a theoretical investigation of the adsorption of alkali metal atoms deposited on ultrathin oxide films. The properties of Li, Na, and K atoms adsorbed on SiO(2)/Mo(112) and of K on MgO / Ag(100) and TiO(2)/Pt(111) have been analyzed with particular attention to the induced changes in the work function of the system, Phi. On the nonreducible SiO(2) and MgO oxide films there is a net transfer of the outer ns electron of the alkali atom to the metal substrate conduction band; the resulting surface dipole substantially lowers Phi.

Observable consequences of formation of Au anions from deposition of Au atoms on ultrathin oxide films.

Charging of metal atoms or clusters on oxide surfaces has important consequences on their chemical and physical properties. Recently it is has been shown that negatively charged gold atoms and clusters form spontaneously from neutral Au atoms deposited on ultrathin MgO films. The formation of anions on the surface remains difficult to prove experimentally.

Nature of point defects on SiO2/Mo(112) thin films and their interaction with Au atoms.

We have studied by means of periodic DFT calculations the structure and properties of point defects at the surface of ultrathin silica films epitaxially grown on Mo(112) and their interaction with adsorbed Au atoms. For comparison, the same defects have been generated on an unsupported silica film with the same structure. Four defects have been considered: nonbridging oxygen (NBO, [triple bond]Si-O(*)), Si dangling bond (E' center, [triple bond]Si(*)), oxygen vacancy (V(O), [triple bond]Si-Si[triple bond]), and peroxo group ([triple bond]Si-O-O-Si[triple bond]), but only the NBO and the V(O) centers are likely to form on the SiO(2)/Mo(112) films under normal experimental conditions.