Fluxionality of gold nanoparticles investigated by Born - Oppenheimer molecular dynamics

The structure and electronic properties of gold nanoparticles (Au 12, Au 13, Au 14, Au 15, Au 20, Au 34, and Au 55) have been investigated using Born-Oppenheimer ab initio molecular dynamic simulations of 50 to 80 ps in order to have an insight in the recently proposed fluxional character of nanosized gold. The dynamic changes in shape, symmetry, and atomic coordination of atoms within clusters, occurring in the time scale of picoseconds, which are characteristic of fluxionality, have been investigated for all the above systems at 300 K. Except for Au 20, all systems have been found to have fluxional properties. The extent and the type of fluxional behavior changed according to the number of atoms constituting the particle. At 300 K Au 12 and Au 13 rapidly generate several different topologies which cyclically interconvert. Au 14 shows a rotation of 8 external gold atoms around a core of six atoms. Au 15 is more rigid, but interestingly shows the interconversion between enantiomeric structures within the time scale of the simulation. Au 20 shows a high stability of the pyramidal topology and is the only one of the investigated systems not to show fluxionality within the assigned temperature and time scale. Au 34 and Au 55 show fluxionality of the outer shell and within the sampled time scale are able to change coordination of the outer shell atoms and thus open and close surface holes. For all the particles in study the structures forming the local minima were isolated and separately optimized, and the electronic properties of the thus obtained structures were analyzed. Fluxionality of gold nano-particles investigated by Born-Oppenheimer molecular dynamics Angelo Vargas, ∗ Gianluca Santarossa, Marcella Iannuzzi, and Alfons Baiker Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Hönggerberg, HCI, 8093 Zurich, Switzerland Institute of Physical Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland (Dated: October 27, 2009)