Journal of Physical Chemistry, Vol.100, No.6, 2053-2061, 1996
Changes of Morphology and Capping of Model Transition-Metal Clusters
We investigate changes of morphology between icosahedra, cuboctahedra, and decahedra in transition metal clusters containing 13, 55, and 147 atoms modeled by two different classes of empirical potential. Highly cooperative processes exist which lead to a fundamental change in structure via a single transition state. As the size increases, these pathways break down into a series of steps, and intermediate stationary points appear; this happens at smaller size for clusters described by the Sutton-Chen potentials. Comparison of our calculated barriers and rates with previous results; from electron microscopy and calculations of diffusion and interlayer transport mechanisms generally gives qualitative agreement. However, neither potential predicts that AU(55) or AU(147) cuboctahedra will be observable experimentally. A combination of substrate interaction and capping probably explains this discrepancy. Finally, we predict that the icosahedral-morphology is likely to be ’frozen in’ at relatively low particle size and that layer by layer growth of Mackay icosahedra is possible via appropriate surface rearrangements.
Keywords:POTENTIAL-ENERGY FUNCTIONS;LENNARD-JONES CLUSTERS;SURFACE SELF-DIFFUSION;STATIONARY-POINTS;NICKEL CLUSTERS;REACTION-PATH;PARTICLES;ENERGETICS;ATOMS;REARRANGEMENTS