title: Metallic icosahedron phase of sodium at terapascal pressures.
abstract: Alkali metals exhibit unexpected structures and electronic behavior at high pressures. Compression of metallic sodium (Na) to 200 GPa leads to the stability of a wide-band-gap insulator with the double hexagonal hP4 structure. Post-hP4 structures remain unexplored, but they are important for addressing the question of the pressure at which Na reverts to a metal. Here, we report the reentrant metallicity of Na at the very high pressure of 15.5 terapascal (TPa), predicted using first-principles structure searching simulations. Na is therefore insulating over the large pressure range of 0.2-15.5 TPa. Unusually, Na adopts an oP8 structure at pressures of 117-125 GPa and the same oP8 structure at 1.75-15.5 TPa. The metallization of Na occurs on the formation of a stable and striking body-centered cubic cI24 electride structure consisting of Na_{12} icosahedra, each housing at its center about one electron that is not associated with any Na ions.
authors: School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China.|State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
authors: Yinwei
authors: Y
authors: Li
authors: State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
authors: Yanchao
authors: Y
authors: Wang
authors: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors: Chris J
authors: CJ
authors: Pickard
authors: Theory of Condensed Matter Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors: Richard J
authors: RJ
authors: Needs
authors: Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, China.
authors: Yi
authors: Y
authors: Wang
authors: State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
authors: Yanming
authors: Y
authors: Ma