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Strain effects on the stabilization of Al ad-atom on graphene oxide(GO)nanosheet as well as its implications for NH3 storage have been investigated using first-principles calculations.The binding energy of Al ad-atom on GO is found to be a false indicator of its stability.Tensile strain is found to be very effective in stabilizing the Al ad-atom on GO.It strengthens the C-O bonds through an enhanced charge transfer from C to O atoms. Interestingly,C-O bond strength is found to be the correct index for Al's stability.Optimally strained Al-functionalized GO binds up to 6 NH3 molecules,while it binds no NH3 molecule in unstrained condition., Comment: 11 pages, 3 figures, 4 tables, Applied Physics Letters (Under Review)

We scrutinize the accuracy of the pseudopotential approximation in density-functional theory (DFT) calculations of surfaces by systematically comparing to results obtained within a full-potential setup. As model system we choose the CO oxidation at a RuO2(110) surface and focus in particular on the adsorbate binding energies and reaction barriers as target quantities for the comparison. Rather surprisingly, the major reason for discrepancy does not result from the neglected semi-core state relaxation in the frozen-core approximation, but from an inadequate description of the local part of the Ru pseudopotential, responsible for the scattering of f like waves. Tiny, seemingly irrelevant, imprecisions appearing in these properties can have a noticeable influence on the surface energetics. At least for the present example, we obtain excellent agreement between both approaches, if the pseudopotential describes these scattering properties accurately., 8 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.html

Monte-Carlo simulation technique has been used to investigate the effect of temperature and adsorbed gases on the composition profile of unsupported Pt-Rh nanocatalysts. For a 2406 atom fcc cubo-octahedral Pt$_{\rm{}50}$Rh$_{\rm{}50}$ nanocatalyst the shell-wise composition for all the eight shells has been simulated. For the temperatures 700 K, 1000 K and 1300 K, the top shell of clean Pt-Rh nanocatalysts is found to be mildly Pt-enriched, while the second shell is Pt-depleted. The Pt concentration of the top shell shows a maximum at T = 1000 K. In presence of a quarter monolayer of adsorbed oxygen the top shell shows Rh enrichment, while all the other shells show Pt-enrichment. This is true for all the three temperatures for which the composition profiles have been studied., 9 pages (LATEX), 4 postscript figures ; Accepted for publication in Physica B