Using classical dynamics simulations, we model the long-lived structural effect of ultraviolet irradiation on amorphous silica. We find a significant increase in density of a model of amorphous silica following localized energy deposition, in agreement with experimental observation. We present evidence that this densification arises as a result of the rapid local cooling that follows irradiation. Similar high density forms of amorphous silica are found following fast quenches of bulk samples. In support of this proposal we demonstrate that very rapidly quenched silica undergoes dilation, rather than compaction, on irradiation.
Monte Carlo simulation studies of reverse micelles of an anionic surfactant, sodium AOT, in a non-polar solvent provide strong evidence that, in the absence of water, these clusters are charge ordered polyhedral shells. The stabilizing energy of these clusters is so large that the entropy of mixing is, in comparison, inconsequential and we predict that, if all waters of hydration could be removed (something not yet accomplished for the sodium salt) then AOT would be insoluble in nonpolar solvents.
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 103 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.
Clusters of hard sphere ions with sufficient size asymmetry to stabilize a tetrahedral structure in the bulk are found to exhibit trivalent polyhedral ground states in clusters of up to roughly 200 ions. The map of cluster ground state structures over the space of cluster size and ion asymmetry is presented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.