title: Predicted novel high-pressure phases of lithium.
abstract: Under high pressure, "simple" lithium (Li) exhibits complex structural behavior, and even experiences an unusual metal-to-semiconductor transition, leading to topics of interest in the structural polymorphs of dense Li. We here report two unexpected orthorhombic high-pressure structures Aba2-40 (40 atoms/cell, stable at 60-80 GPa) and Cmca-56 (56 atoms/cell, stable at 185-269 GPa), by using a newly developed particle swarm optimization technique on crystal structure prediction. The Aba2-40 having complex 4- and 8-atom layers stacked along the b axis is a semiconductor with a pronounced band gap >0.8 eV at 70 GPa originating from the core expulsion and localization of valence electrons in the voids of a crystal. We predict that a local trigonal planar structural motif adopted by Cmca-56 exists in a wide pressure range of 85-434 GPa, favorable for the weak metallicity.
authors.affiliation: State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Lv
authors.forename: Yanchao
authors.initials: Y
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Zhu
authors.forename: Yanming
authors.initials: Y
authors.lastname: Ma