Fig. 1.

Bimodal distribution of structures sampled in a Monte Carlo simulation of (H₂O)₈ reported in ref. 14. Results were obtained by quenching to their local minima structures sampled at the temperature at which the specific heat has its maximum. The low-energy peak is due to cubic structures that dominate the “solid” phase, and the high-energy peak is due to noncubic structures (one of which is shown) that dominate the “liquid” phase. In molecular dynamics simulations on a single (H₂O)₈ cluster, the 2 phases oscillate on a picosecond timescale (13). Moberg et al. (1) interpret the vibrational spectra of clusters containing about 90 to 150 water molecules as being due to analogous oscillations between amorphous clusters and clusters with ice I cores.