Ground-State Structures of Ice at High-Pressures

الأصل · EN

Ab initio random structure searching based on density functional theory is used to determine the ground-state structures of ice at high pressures. Including estimates of lattice zero-point energies, ice is found to adopt three novel crystal phases. The underlying sub-lattice of O atoms remains similar among them, and the transitions can be characterized by reorganizations of the hydrogen bonds. The symmetric hydrogen bonds of ice X and Pbcm are initially lost as ice transforms to structures with symmetries Pmc2₁ (800 - 950 GPa) and P2₁ (1.17 TPa), but they are eventually regained at 5.62 TPa in a layered structure C2/m. The P2₁ → C2/m transformation also marks the insulator-to-metal transition in ice, which occurs at a significantly higher pressure than recently predicted.