Download Computational Studies of Transition Metal Nanoalloys by Lauro Oliver Paz Borbón PDF

By Lauro Oliver Paz Borbón

The concentration of this thesis is the computational modelling of transition steel bimetallic (nanoalloy) clusters. extra in particular, the examine of Pd-Pt, Ag-Pt, Au-Au and Pd-Au as a couple of tens of atoms within the gasoline part. the writer used a mixture of worldwide optimization thoughts - coupled with a Gupta-type empirical many-body capability - and Density useful concept (DFT) calculations to review the constructions, bonding and chemical ordering, in addition to examine the chemisorptions of hydrogen and carbon monoxide on bimetallic clusters. This learn is very suitable to experimental catalytic reviews and has ended in greater than seven courses in foreign journals.

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Freund, J. Phys. Chem. B 107, 255 (2003) 53. M. Walter, J. Akola, O. Lopez-Acevedo, G. J. L. Whetten, H. Grönbeck, H. Häkkinen, PNAS 105, 9157 (2008) 54. M. Bäumer, J. M. Neyman, N. Rösch, G. -J. Freund, Phys. Chem. Chem. Phys. 9, 3541 (2007) 55. D. Bazin, Macro. Res. 17, 230 (2006) 56. L. J. Madix, Surf. Sci. 237, 1 (1990) 57. F. D. W. Goodman, Surf. Sci. 175, 215 (1986) 58. A. Gravil, H. Toulhoat, Surf. Sci. 430, 176 (1999) Chapter 2 Theoretical Background and Methodology In this chapter the different approaches followed in order to model metal nanoparticles are described.

4 DFT Calculations 43 Fig. 7 Double tetrahedral Pt (light color) core the Dh–cp(DT) structure for various compositions. At low Pt concentrations, some Pd (dark color) atoms are shown for completeness results indicate that the mixed Dh–cp(DT) motif seems to be preferred in this size range, with a somewhat enhanced stability at size 34 and 36. However, they were unable to single out a cluster in which structural stability was associated with electronic shell closure, as the density of states around the Fermi level always come out rather smooth, confirming the metallic character of these systems.

For this reason, the expressions ‘‘putative GM’’ or ‘‘lowest-energy structure’’ are used when discussing the results of DFT calculations. 4 Energetic Analysis In order to analyse cluster stability, some energetic quantities need to be defined. 4 Energetic Analysis 29 where Vclus is the total potential energy of the cluster (pure metal or bimetallic) and N is the total number of atoms in the cluster. e. lower EbGupta values would indicate less favourable atomic arrangements). Another criterion for determining relative stability (both at the Gupta and DFT level) is the second difference in binding energy, D2 Eb ðNÞ.

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