HR: 09:04h
AN: MR11A-05    [Abstracts]
TI: Stability of H₂O ice polymorphs at high pressure
AU: * Caracas, R
EM: razvan.caracas@ens-lyon.fr
AF: Ecole Normale Superieure de Lyon, Laboratory of Earth Sciences UMR 5570 46, allée d'Italie, Lyon, 69364, France
AB: We employ the generalized gradient approximation within the density functional theory as implemented in the ABINIT package [1] to investigate the high-pressure behavior of H₂O ice. We find that ice VIII is dynamically stable to at least 100 GPa. From static (0K) calculations we show that ice X is more stable than ice VIII above 80- 100 GPa. Ice X is dynamically stable in the 120-400 GPa pressure range. Below 120 GPa it is characterized by one unstable flat phonon band, which leads to the amorphization of the structure. In its dynamical stability field, ice X shows a softening of the lowest phonon mode in M (=1/2 1/2 0) under compression, which becomes unstable above 400 GPa. The instability corresponds to the bending of the O-H-O angle. The structure that results after the lock-in of the unstable mode agrees well with the Pbcm orthorhombic structure obtained from molecular-dynamics calculations [2]. We propose a high-pressure low-temperature phase-transition sequence as ice VIII - amorphous - ice X - ice Pbcm. [1] Gonze et al., Comp. Mat. Sci. 25, 478 (2002); Z. Kristall. 220, 558 (2005). [2] Benoit et al., Phys. Rev. Lett., 76, 2934, 1996.
DE: 3924 High-pressure behavior
DE: 5422 Ices
DE: 6020 Ices
DE: 6045 Physics and chemistry of materials
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting