Computational methodology for structure prediction. - Small Au/MgO(001)
clusters: leaflets, cages and more. - Large Au/MgO(001) clusters: compact
structures.
Structures of gold nanoparticles on flat and stepped oxide surfaces
Riccardo Ferrando Dipartimento di Fisica, Università di Genova, Italy
GDR OR-NANO, Poitiers, March 19-21, 2012
MgO(001) surface
a perfect checkerboard of Mg (or Ca) and O atoms
MgO(001) surface
Metal atoms adsorb on top of oxygen atoms
Outline
- Computational methodology for structure prediction - Small Au/MgO(001) clusters: leaflets, cages and more - Large Au/MgO(001) clusters: compact structures - Small Au clusters on stepped MgO(001)
Computational methodology Development of an atom-atom interaction potential Global optimization of the PES, construction of a database of structures Local relaxation at the DFT level (GGA-PBE functional, check by LDA)
Model potential
metal oxide
metal-metal metal-oxide
E = Emet + Emet-MgO
• Metal-metal interactions semi-empirical tight-binding approach • Metal-MgO(001) interactions analytical function fitted to first principle calculations
Global optimization searches Basin hopping: Monte Carlo-Metropolis procedure + local minimisation Original PES Transformed PES
DRAWBACK: still not satisfactory in exploring multiple-funnel surfaces
Beyond basin hopping: - Parallel excitable walkers algorithm - HISTO algorithm
Small (11 ≤ N ≤ 32) Au/MgO(001) clusters
• Neutral
Au clusters on defect-free MgO(001)
• Compact structures searched for by global optimization • “Hand-made” 2D and cage structures • DFT relaxation GGA/PBE -- underbinding metal-metal interactions LDA -- overbinding metal-metal interactions
Weird structures of small Au/MgO clusters Au32
Pyramidal open cages [R. Ferrando, G. Barcaro, A. Fortunelli, PRL (2009)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Structural motifs of small Au/MgO clusters
[R. Ferrando, G. Barcaro, A. Fortunelli, PRB (2011)]
Au/MgO clusters: size-dependent transitions Leaflet
Compact
Open cage
Tetrahedral
DFT (PBE) N= 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Transition to compact structures for N>40 [R. Ferrando, G. Barcaro, A. Fortunelli, PRL (2009), PRB (2011)]
Larger (N > 50) Au/MgO(001) clusters
• For
N
