  In our earlier study of Ag island coarsening on Ag(111) surface using kinetic
Monte Carlo (KMC) simulations we found that during early stages coarsening
proceeds as a sequence of selected island sizes resulting in peaks and valleys
in the island-size distribution and that this selectivity is independent of
initial conditions and dictated instead by the relative energetics of edge-atom
diffusion and detachment/attachment processes and by the large activation
barrier for kink detachment. In this paper we present a detailed analysis of
the shapes of various island sizes observed during these KMC simulations and
show that selectivity is due to the formation of kinetically stable island
shapes which survive longer than non-selected sizes, which decay into nearby
selected sizes. The stable shapes have a closed-shell structure - one in which
every atom on the periphery having at least three nearest neighbors. Our KMC
simulations were carried out using a very large database of processes
identified by each atom's unique local environment, the activation barriers of
which were calculated using semi-empirical interaction potentials based on the
embedded-atom method.
