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Abstract
Nanoscale structures are increasingly applied in the design of catalysts and electronic devices. A theoretical understanding of the basic properties of such systems is enabled through modern electronic structure methods such as density functional theory. This thesis describes the development of efficient approaches to density functional theory and the application of these methods to metal nanoparticles.
We describe the formalism and implementation of localized atomcentered basis sets within the projector augmented wave method. Basis sets allow for a dramatic increase in performance compared to planewave or realspace methods, but sacrifice accuracy in doing so. This approach is implemented in the GPAW code where it complements the existing realspace approach. For both the realspace and basis set methods we implement parallel code to adapt GPAW for largescale calculations on the BlueGene/P architecture. Realspace calculations are performed to investigate the convergence of chemical properties of Au and Pt clusters toward the bulk limit. Specically we study chemisorption of O and CO on cuboctahedral clusters up to 1415 atoms using up to 65536 CPU cores. Small clusters almost universally bind more strongly than large ones. This can be understood mostly as a geometric eect. Convergence of chemisorption energies within 0.1 eV of bulk values happens at about 200 atoms for Pt and 600 atoms for Au. Particularly for O on Au, large variations due to electronic effects are seen for smaller clusters. The basis set method is used to study the electronic effects for the contiguous range of clusters up to several hundred atoms. The selectrons hybridize to form electronic shells consistent with the jellium model, leading to electronic magic numbers for clusters with full shells. Large electronic gaps and jumps in Fermi level near magic numbers can lead to alkalilike or halogenlike behaviour when maingroup atoms adsorb onto gold clusters. A nonselfconsistent NewnsAnderson model is used to more closely study the chemisorption of maingroup atoms on magicnumber Au clusters. The behaviour at magic numbers can be understood from the location of adsorbateinduced states relative to the Fermi level. The relationship between geometric and electronic eects in Au is studied by rough firstprinciples simulated annealings with up to 150 atoms. Nonmagic clusters are found to deform considerably, reducing the total energy through the creation of gaps. Clusters larger than 100 atoms can elongate systematically by up to 15 %. This demonstrates a complex interdependence between electronic and geometric structure in a size regime which in most cases has been studied semiempirically.
We describe the formalism and implementation of localized atomcentered basis sets within the projector augmented wave method. Basis sets allow for a dramatic increase in performance compared to planewave or realspace methods, but sacrifice accuracy in doing so. This approach is implemented in the GPAW code where it complements the existing realspace approach. For both the realspace and basis set methods we implement parallel code to adapt GPAW for largescale calculations on the BlueGene/P architecture. Realspace calculations are performed to investigate the convergence of chemical properties of Au and Pt clusters toward the bulk limit. Specically we study chemisorption of O and CO on cuboctahedral clusters up to 1415 atoms using up to 65536 CPU cores. Small clusters almost universally bind more strongly than large ones. This can be understood mostly as a geometric eect. Convergence of chemisorption energies within 0.1 eV of bulk values happens at about 200 atoms for Pt and 600 atoms for Au. Particularly for O on Au, large variations due to electronic effects are seen for smaller clusters. The basis set method is used to study the electronic effects for the contiguous range of clusters up to several hundred atoms. The selectrons hybridize to form electronic shells consistent with the jellium model, leading to electronic magic numbers for clusters with full shells. Large electronic gaps and jumps in Fermi level near magic numbers can lead to alkalilike or halogenlike behaviour when maingroup atoms adsorb onto gold clusters. A nonselfconsistent NewnsAnderson model is used to more closely study the chemisorption of maingroup atoms on magicnumber Au clusters. The behaviour at magic numbers can be understood from the location of adsorbateinduced states relative to the Fermi level. The relationship between geometric and electronic eects in Au is studied by rough firstprinciples simulated annealings with up to 150 atoms. Nonmagic clusters are found to deform considerably, reducing the total energy through the creation of gaps. Clusters larger than 100 atoms can elongate systematically by up to 15 %. This demonstrates a complex interdependence between electronic and geometric structure in a size regime which in most cases has been studied semiempirically.
Original language  English 

Publisher  Technical University of Denmark, Center for AtomicScale Materials Physics 

Number of pages  172 
Publication status  Published  2011 
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 1 Finished

Katalytiske og elektroniske egenskaber af metalnanopartikler
Larsen, A. H., Jacobsen, K. W., Thygesen, K. S., Rossmeisl, J., Manninen, M. J. & Grönbeck, H.
Technical University of Denmark
01/09/2008 → 20/01/2012
Project: PhD