Al13- is a cluster known for the pronounced stability that arises from coincident closures of its geometric and electronic shells. We present experimental evidence for a very stable cluster corresponding to Al13I-. Ab initio calculations show that the cluster features a structurally unperturbed Al13- core and a region of high charge density on the aluminum vertex opposite from the iodine atom. This ionically bound magic cluster can be understood by considering that Al13 has an electronic structure reminiscent of a halogen atom. Comparisons to polyhalides provide a sound explanation for our chemical observations.

Aluminum Aluminum I 2100Formation of Al 13 I -: Evidence for the Superhalogen Character of Al 13 . -Reactions of Al clusters with HI in a fast-flow tube apparatus lead to the formation of the very stable Al13Icluster. DFT calculations show that the cluster features a structurally unperturbed core and a region of high charge density on the Al vertex opposite from the iodine atom. This ionically bound magic cluster can be understood by considering that Al 13 has an electronic structure reminiscent of a halogen atom. -(BERGERON, D. E.; CASTLEMAN*, A. W.

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby Al(n)X(-) generation is energetically favorable. Tandem reaction experiments allowed us to establish that for Al(n)Cl(-), Al(n)I(-), and Al(n)I(2) (-), species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters' electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. Lowest energy structures for Al(13)X(-) were found to feature icosahedral Al(13) units with the halogen atom located at the on-top site. The charge density of the highest occupied molecular orbital in these clusters is heavily dependent on the identity of X. The dependence of reactivity on the clusters' charge state is also discussed. In addition, we address the enhanced stability of Al(13)I(-) and Al(13)I(2) (-), arguing that the superhalogen behavior of Al(13) in these clusters can provide unique opportunities for the synthesis of novel materials with saltlike structures.

Recent advances in graphics processing unit (GPU) hardware and improved efficiencies of atomistic simulation programs allow for the screening of a large number of polymers to predict properties that require running and analyzing long molecular dynamics (MD) trajectories. This paper outlines a MD simulation workflow based on GPU MD simulation and the refined optimized potentials for liquid simulation (OPLS) OPLS3e force field to calculate glass transition temperatures (T gs) of 315 polymers for which Bicerano reported experimental values [BiceranoJ. Bicerano, J. Prediction of Polymer PropertiesMarcel Dekker Inc.New York1996]. Applying the workflow across this large set of polymers allowed for a comprehensive evaluation of the protocol performance and helped in understanding its merits and limitations. We observe a consistent trend between predicted T g values and empirical observation across several subsets of polymers. Thus, the protocol established in this work is promising for exploring targeted chemical spaces and aids in the evaluation of polymers for various applications, including composites, coatings, electrical casings, etc. During the stepwise cooling simulation for the calculation of T g, a subset of polymers clearly showed an ordered structure developing as the temperature decreased. Such polymers have a point of discontinuity on the specific volume vs temperature plot, which we associate with the melting temperature (T m). We demonstrate the distinction between crystallized and amorphous polymers by examining polyethylene. Linear polyethylene shows a discontinuity in the specific volume vs temperature plot, but we do not observe the discontinuity for branched polyethylene simulations.