(KCl)32 and the possibilities for glassy clusters

Abstract

The alkali halide cluster (KCl)₃₂ is demonstrated to be large enough to exhibit ordered and highly disordered structures. The disordered high‐energy stable packings of (KCl)₃₂ are identified as amorphous structures. We term the large collection of amorphous (KCl)₃₂ structures the ‘‘microamorphous’’ state, on the basis that they are as disordered as the bulk glass phase. Liquid (KCl)₃₂ was quenched to investigate how fast the cooling rate must be to trap (KCl)₃₂ in one of the high‐energy amorphous structures. Even at unrealistically fast cooling rates, (KCl)₃₂ was able to locate its microcrystal structure. A shielded Coulomb interaction potential was used to test whether reducing the range of the pairwise potential would make it possible to prepare amorphous binary clusters. Several different values of the shielding range were tested. These results are discussed in terms of the structure of the underlying potential energy surface. A short study was conducted of the temperature dependence of the time it takes, on average, for supercooled (KCl)₃₂ to relax into the crystalline regions of its potential energy surface. Lastly, we rationalize, in terms of the potential energy surface, the qualitative temperature dependence of the heat capacity for both the first‐order and glass transitions.