Inorganic Nanotubes Stabilized by Ion Size Asymmetry: Energy Calculations for AgI Clusters

Using an accurate “rigid ion” potential for AgI developed by Parrinello, Rahman, and Vashishta, we have calculated the energy of AgI clusters containing up to 10 3 ions. Unlike the smaller halides such as Cl and Br, we find that the lowest energy clusters of AgI are trivalent polyhedral shells, instead of crystal fragments, for clusters up to around 100 ions. Most of these polyhedral minima take the form of nanotubes. We argue that the enhanced stability of such structures in AgI clusters arises from the same ion asymmetry that stabilizes the wurtzite structure in the bulk crystal.