Computational Free Energy Studies of a New Ice Polymorph Which Exhibits Greater Stability than Ice I_h

The absolute free energies of several ice polymorphs were calculated using thermodynamic integration. These polymorphs are predicted by computer simulations using a variety of common water models to be stable at low pressures. A recently discovered ice polymorph that has as yet only been observed in computer simulations (Ice-i) was determined to be the stable crystalline state for all the water models investigated. Phase diagrams were generated, and phase coexistence lines were determined for all of the known low-pressure ice structures. Additionally, potential truncation was shown to play a role in the resulting shape of the free energy landscape.