THERMALLY-INDUCED FRAGMENTATION IN AN ICE LATTICE

Molecular dynamics simulation of isobaric heating of an H2O lattice wi th diamond cubic structure reveals a distinct two-step sequence of hyd rogen-bond breaking in a temperature range clearly below the melting p oint. Partial breakage, signaled by an abrupt increase in local atomic coordination and the coupling of intermolecular torsions with intramo lecular angle bending, first occurs and leaves the lattice in a fragme nted but still ordered state. This is then followed by full breakage a t a temperature about 20-30 K higher, bringing the lattice to an orien tationally disordered state characterized by a vibrational spectrum si milar to that of water.