Øyvind Borck

First-principles study of the adsorption of methanol at the α-Al2O3(0001) surface

We present density functional theory calculations of methanol molecular adsorption at the (0001) surface of alpha-Al2O3, for methanol coverages of 1/4 to 1 monolayer (ML). Adsorption energies, adsorption-induced restructuring of the surface, and induced changes to the electronic structure are calculated. We find that methanol bonds with its O atom to Al atoms at the alpha-Al2O3(0001) surface with an adsorption energy of 1.23 eV at coverage 1/4 ML, decreasing with coverage to 1.03 eV at 1 ML coverage. From calculations of the relaxed adsorption geometry and the angular dependence of the total energy, we predict an orientation of the adsorbed methanol molecule that has the molecular COH plane tilted away from the surface normal. The adsorption of methanol significantly restructures alpha-Al2O3(0001), especially for the outermost Al layer. Upon adsorption a small charge transfer from the molecule to the substrate takes place.

Van der Waals density functional calculations of binding in molecular crystals

A recent paper [J. Chem. Phys. 132 (2010) 134705] illustrated the potential of the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92 (2004) 246401] for efficient first-principle accounts of structure and cohesion in molecular crystals. Since then, modifications of the original vdW-DF version (identified as vdW-DF1) have been proposed, and there is also a new version called vdW-DF2 [Phys. Rev. B 82 (2010) 081101(R)], within the vdW-DF framework. Here we investigate the performance and nature of the modifications and the new version for the binding of a set of simple molecular crystals: hexamine, dodecahedrane, C60, and graphite. These extended systems provide benchmarks for computational methods dealing with sparse matter. We show that a previously documented enhancement of non-local correlations of vdW-DF1 over an asymptotic atom-based account close to and a few A beyond binding separation persists in vdW-DF2. The calculation and analysis of the binding in molecular crystals require appropriate computational tools. In this paper, we also present details on our real-space parallel implementation of the vdW-DF correlation and on the method used to generate asymptotic atom-based pair potentials based on vdW-DF.

Adsorption of methanol and methoxy on the α-Cr2O3(0001) surface

We present density functional theory calculations of methanol and methoxy adsorption at the Cr-terminated ?-Cr2O3(0001) surface. We report on the equilibrium geometries of the adsorbed methanol and methoxy molecules, analyse the bonding to the surface, and discuss the dissociation energetics of methanol into methoxy on the surface. We found that methanol adsorbs with its O atom situated above a threefold coordinated hollow site in the surface O layer at a distance of 2.12?? from the nearest-neighbour Cr atom, and with a calculated adsorption energy of 0.82?eV. For the methoxy molecule we found the optimum adsorption geometry to be with the methoxy O on top of a Cr atom and with the CO-axis tilted away from the surface normal by ~55?. Methoxy is strongly bound to the surface with an estimated adsorption energy of 3.3?eV.

Methylbenzenes on graphene

We present a theory study of the physisorption of the series of methylbenzenes (toluene, xylene and mesitylene), as well as benzene, on graphene. The aim is two fold: we provide data that will be used as input to larger-scale methods like molecular-dynamics simulations, and at the same time we enhance the basic understanding of graphene used as a material for sensors and as an idealized model for the carbon in active carbon filters. The molecules are studied in a number of positions and orientations relative to graphene, using density functional theory with the van der Waals functional vdW-DF. The molecules are adsorbed fractional coverage. We focus on the vdW-DF1 and vdW-DF-cx functionals, and find that the binding energy of the molecules on graphene grows linearly with the number of methyl groups, at the rate of 0.09 eV (vdW-DF1) to 0.11 eV (vdW-DF-cx) per added methyl group. We further find that the orientation of the methyl groups of the molecules relative to graphene is at least as important as the lateral position of the whole molecule on graphene.

Adsorption of methylamine on Ni3Al(111) and NiAl(110)-a high resolution photoelectron spectroscopy and density functional theory study

Methylamine adsorption on the ordered Ni(3)Al(111) and NiAl(110) surfaces has been investigated by high resolution photoelectron spectroscopy and density functional theory calculations. Methylamine adsorbs molecularly at both surfaces at low temperature (90 K). The experiments show that methylamine interacts with the surface aluminium atoms on both surfaces, resulting in a positive binding energy shift relative to the Al 2p bulk contributions. A shift towards lower binding energy is also observed on NiAl(110) attributed to first and second layer surface Al atoms not bonded to methylamine. According to total energy calculations methylamine binds through its N atom to Al on-top sites on NiAl(110) while the Ni on-top site is found to be slightly preferred over the Al on-top site on Ni(3)Al(111). Calculated adsorbate induced shifts are, however, in good agreement with the experimental values only when methylamine is situated in the Al on-top site on both surfaces. In both cases, a lone pair bonding mechanism is found.

Involving High School Students in Computational Physics University Research: Theory Calculations of Toluene Adsorbed on Graphene

To increase public awareness of theoretical materials physics, a small group of high school students is invited to participate actively in a current research projects at Chalmers University of Technology. The Chalmers research group explores methods for filtrating hazardous and otherwise unwanted molecules from drinking water, for example by adsorption in active carbon filters. In this project, the students use graphene as an idealized model for active carbon, and estimate the energy of adsorption of the methylbenzene toluene on graphene with the help of the atomic-scale calculational method density functional theory. In this process the students develop an insight into applied quantum physics, a topic usually not taught at this educational level, and gain some experience with a couple of state-of-the-art calculational tools in materials research.