New High-Pressure Phase of Ice

Abstract
Based on ab initio constant pressure molecular dynamics simulation, we predict a new phase transition in ice from ice X to a new phase (ice XI) at 3Mbar and room temperature. Ice XI preserves the symmetric hydrogen bond and is a wide gap insulator up to and beyond 7 Mbar. This new phase is stable up to 2000 K at 4 Mbar, where the system shows large protonic diffusion.