title: Lithium hydroxide, LiOH, at elevated densities.
abstract: We discuss the high-pressure phases of crystalline lithium hydroxide, LiOH. Using first-principles calculations, and assisted by evolutionary structure searches, we reproduce the experimentally known phase transition under pressure, but we suggest that the high-pressure phase LiOH-III be assigned to a new hydrogen-bonded tetragonal structure type that is unique amongst alkali hydroxides. LiOH is at the intersection of both ionic and hydrogen bonding, and we examine the various ensuing structural features and their energetic driving mechanisms. At P = 17 GPa, we predict another phase transition to a new phase, Pbcm-LiOH-IV, which we find to be stable over a wide pressure range. Eventually, at extremely high pressures of 1100 GPa, the ground state of LiOH is predicted to become a polymeric structure with an unusual graphitic oxygen-hydrogen net. However, because of its ionic character, the anticipated metallization of LiOH is much delayed; in fact, its electronic band gap increases monotonically into the TPa pressure range.
authors.affiliation: School of Physics and Astronomy and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hermann
authors.affiliation: Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: N W
authors.initials: NW
authors.lastname: Ashcroft
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Roald
authors.initials: R
authors.lastname: Hoffmann