Fig. 2: Structures and properties of high-pressure phases at 0 K.
From: Thermodynamics of high-pressure ice phases explored with atomistic simulations
a The structures of the ice phases considered. The simulation supercells used in DFT calculations are indicated using black boxes. b 0 K enthalpy curves for different ice phases predicted by the PBE DFT functional. c The length of the edge vectors of the simulation supercell (lxx, lyy and lzz) for X(orthorhombic), X(cubic) and Pbcm phases at 0 K. All three cell parameters for X(cubic) are the same, so the three orange curves overlap; two edge lengths for the X(orthorhombic) cell are the same, so two blue curves overlap; and for Pbcm there are three different cell parameters. The simulation supercells used for X(cubic) and X(orthorhombic) have 2 water molecules, while the Pbcm supercell has 4 molecules (see panel a), so the cell parameters for the Pbcm supercell in two directions have been divided by \(\sqrt{2}\).
