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. (C) 2017 Elsevier B.V. All rights reserved.

The interaction between dihydrogen sulfide (H2S) and Cr and CrO terminated Cr2O3(0001) surfaces is studied with density functional theory (DFT). Calculations are carried out at 0.50 and 1.0monolayer (M/L) adsorbate coverages. We find that the reactivity of H2S and its dissociated species is stronger to the Cr terminated surface than to the surface terminated by CrO groups. For coverages between 0.5 and 1.0M/L, the dissociative adsorption as H and HS species is found to be favored on the Cr terminated surface, with adsorption energies around 0.9eV when CrS fragments are formed, with S located above the hollow fcc site of the surface O atoms. Calculated adsorption energies are in the range 0.4–0.6eV for molecular adsorption on the Cr terminated surface. Activation energies for dissociative adsorption are investigated to be in the range 0.3–0.5eV at 0.5M/L coverage and in the range 0.6–1.0eV at 1.0M/L coverage. Full decompositive adsorption appears to be favored at coverages below 0.5M/L. This indicates the likelihood and conditions for this molecule to lead to corrosion on the surface.

Density functional theory calculations show that H2, Cl2, and HCl molecules chemisorb dissociatively on the Cr2O3(0001) surface, which can be terminated by Cr atoms, Chromyl groups (Cr=O), or O atoms. It is investigated that these molecules energetically prefer to adsorb dissociatively than in molecular form. Several dissociative adsorption sites have been considered for all the molecules on all the differently terminated surfaces and the corresponding adsorption energies are calculated. Dissociation energy barriers are estimated with the nudged elastic band method. Notable results from the dissociative adsorptions of Cl2 and H2 are the formation of a CrCl2 complex on the Cr terminated surface, and H2O complex on the O and the Cr=O terminated surfaces, and a H2O layer on the Cr=O terminated surface. Dissociative adsorption of HCl is less favored on the Cr=O and O terminated surfaces than on the Cr terminated surface.

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.

Adsorption of atomic H, Cl, and S on the chromyl (Cr=O), oxygen (O), and chromium (Cr) terminated alpha-Cr2O3(0001) surfaces is investigated using density functional theory (DFT). Adsorption of H is strongest on the Cr=O and O terminated surfaces. H preferably binds to O atoms of these surfaces. Adsorption of Cl and S atoms is strongest on the Cr terminated surface where the atoms preferably bond to Cr. Geometry preferences are explained by electronic structure analysis. Adsorption to Cr on the O terminated surface results in significant outward relaxation of the Cr atoms, causing significant bond breaking on the surface. (C) 2011 Elsevier Ltd. All rights reserved.

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 Å 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.

Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young's modulus of 1.5 GPa and a Poisson ratio approximate to 0.1. These values suggest interpretation of the molecular monolayer as a porous material-in marked congruence with our microscopic observations.

Received 6 December 2010DOI:https://doi.org/10.1103/PhysRevB.82.239903©2010 American Physical Society

Adsorption of methanol on clean Pd(110) and on an alloyed Ag/Pd(110) surface has been studied by high-resolution photoelectron spectroscopy. On Pd(110) two different chemisorbed methanol species were observed for temperatures up to 200K, with the one at lower binding energy remaining at low coverage. These species were attributed to methanol adsorbed in two different adsorption sites on the Pd(110) surface. As is well established for this system, heating to 250K resulted in decomposition of methanol into CO. The adsorption and decomposition behaviour of methanol on the Ag/Pd(110) surface alloy formed by depositing Ag on Pd(110) at elevated temperature was similar to that of the pure Pd(110) surface. This suggests that the amount of Ag present in the Pd(110) surface in this study does not affect the decomposition behaviour of methanol as compared to pure Pd(110). Complementary density functional theory calculations also show little influence of Ag on the binding of methanol to Pd. These calculations predict an on-top adsorption site for low methanol coverages.

Adsorption of CO on metal atoms surfaces is one of the most thoroughly studied adsorption systems. It is a prototypical model system for investigating molecular adsorption, and of fundamental importance in many catalytic reactions. However, real catalysts often consists of several components, and offer geometric and electronic properties different from the elemental surfaces. The Ni3Al(111) surface is a very attractive model system for theoretical and experimental studies of adsorption, as it has an ordered and well-defined surface [1]. Density functional theory (DFT) calculations have become a valuable tool in predicting the properties of clean and adsorbate covered surfaces. However, there are some well known cases where DFT fail to predict the correct adsorption site for CO on a metal surface, notably the Pt(111), Rh(111), and Cu(111) surfaces [2]. Additional information can then be very useful, for example it has been shown that the correct adsorption site for CO on Rh(111) can be predicted by comparing theoretically obtained C 1s core level binding energy shifts to experimentally obtained shifts [3]. In the work presented here we use this approach to characterise the CO adsorption on the Ni3Al(111) surface. We have studied the adsorption of CO on the Ni3Al(111) surface using DFT and high-resolution photoemission spectroscopy (HR-PES). Previous studies of CO on Ni3Al(111) have shown that CO adsorbs in Ni-dominated sites [5–8]. In the present study, a new contribution in the Al 2p photoemission spectra was observed. The DFT calculations predict that CO adsorb in Ni hollow sites at low coverage, and that the adsorption induces a large inward relaxation of nearby surface Al atoms. The calculated Al 2p core level binding energy shifts compare well with the experimental values and reveal that CO adsorption in Ni sites induce core level binding energy shifts in nearby Al atoms. The C 1s spectra has one peak at low coverage, assigned

The adsorption of CO on ${\text{Ni}}_{3}\text{Al}(111)$ has been studied using high-resolution photoemission spectroscopy and density functional theory. Despite the fact that CO binds to Ni dominated sites only at this surface, CO adsorption induces a shifted contribution in the $\text{Al}\text{ }2p$ core-level spectra. This contribution moves toward higher binding energy upon increasing CO coverage. The calculations give $\text{Al}\text{ }2p$ core-level binding energy shifts in good agreement with the experimental values and show that adsorption of CO in the Ni sites induces core-level binding energy shifts for nearby Al atoms located in the two outermost surface layers. The surface Al atoms relax inward upon CO adsorption. At low CO coverage only one peak is observed in the $\text{C}\text{ }1s$ spectra. This contribution is assigned to CO adsorbed in Ni threefold hollow sites. The calculations predict that CO adsorbs in the hollow sites for coverages up to 0.50 ML with a strong preference for the hcp site above a second layer Al atom at low coverage. At higher CO coverage, an additional contribution appears in the $\text{C}\text{ }1s$ spectra whereas the other contribution shifts toward higher binding energies. The theoretical results suggest that this behavior is originating from the occupation of Ni on top and Ni bridge sites in addition to hollow sites.

Methylamine adsorption on the ordered Ni3Al(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 Ni3Al(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.

The adsorption of methanol and methoxy on NiAl(110) and Ni3Al(111) has been investigated using density functional theory (DFT). Optimised adsorption geometries and core level shifts are presented. On both surfaces we find that methanol binds to the Al on-top site via its oxygen atom and with the C–O axis tilted away from the surface normal. Methoxy also shows a preference for Al-dominated sites. On NiAl(110), we predict that methoxy adsorbs with its oxygen atom in the Al–Al bridge site, while it is determined to be adsorbed with its oxygen atom in a 2Ni+Al hollow site on Ni3Al(111), closer to Al than Ni. Surface and adsorbate induced binding energy shifts in the Al 2p states are calculated and found to be in good agreement with experimental high resolution photoelectron spectroscopy results.

The adsorption of methanol on Ni3Al(111) and NiAl(110) has been studied using high resolution photoemission spectroscopy (HR-PES) and density functional theory (DFT). Both methanol and methoxy are formed on these surfaces after the initial methanol exposure at low temperatures. Heating to 200K leads to further formation of methoxy. On NiAl(110) two different methoxy species are observed where the first is formed upon methanol adsorption, and the other results from methanol decomposition during heating. The DFT calculations show that methanol and methoxy interacts with the Al atoms on both surfaces. Methanol is found to bond through the oxygen atom to the Al on-top site on Ni3Al(111) and NiAl(110) with the C–O axis tilted with respect to the surface normal. On Ni3Al(111) methoxy is situated in a 2Ni+Al hollow site, whereas on NiAl(110) the Al–Al bridge site is preferred.

Øyvind Borck,1,2 Per Hyldgaard,2,3 and Elsebeth Schröder2 1Department of Physics, Norwegian University of Science and Technology, NO-7034 Trondheim, Norway 2Applied Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden 3Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden Received 24 August 2006; revised manuscript received 9 November 2006; published 2 January 2007