title: Stable all-nitrogen metallic salt at terapascal pressures.
abstract: The phase diagram and equation of state of dense nitrogen are of interest in understanding the fundamental physics and chemistry under extreme conditions, including planetary processes, and in discovering new materials. We predict several stable phases of nitrogen at multi-TPa pressures, including a P4/nbm structure consisting of partially charged N(2)(δ+) pairs and N(5)(δ-) tetrahedra, which is stable in the range 2.5-6.8 TPa. This is followed by a modulated layered structure between 6.8 and 12.6 TPa, which also exhibits a significant charge transfer. The P4/nbm metallic nitrogen salt and the modulated structure are stable at high pressures and temperatures, and they exhibit strongly ionic features and charge density distortions, which is unexpected in an element under such extreme conditions and could represent a new class of nitrogen materials. The P-T phase diagram of nitrogen at TPa pressures is investigated using quasiharmonic phonon calculations and ab initio molecular dynamics simulations.
authors.affiliation: Department of Physics and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China and Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany and Theory of Condensed Matter Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Miguel
authors.initials: M
authors.lastname: Martinez-Canales
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Klug
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Pickard
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Needs