title: Emergence of novel hydrogen chlorides under high pressure.
abstract: HCl is a textbook example of a polar covalent molecule, and has a wide range of industrial applications. Inspired by the discovery of unexpected stable sodium and potassium chlorides, we performed systematic ab initio evolutionary searches for all stable compounds in the H-Cl system at pressures up to 400 GPa. Besides HCl, four new stoichiometries (H2Cl, H3Cl, H5Cl and H4Cl7) are found to be stable under pressure. Our predictions substantially differ from previous theoretical studies. We evidence a high significance of zero-point energy in determining phase stability. The newly discovered compounds display a rich variety of chemical bonding characteristics. At ambient pressure, H2, Cl2and HCl molecular crystals are formed by weak intermolecular van der Waals interactions, and adjacent HCl molecules connect with each other to form asymmetric zigzag chains, which become symmetric under high pressure. In H5Cl, triangular H3+cations are stabilized by electrostatic interactions with the anionic chloride network. Further increase of pressure drives H2dimers to combine with H3+cations to form H5+units. We also found chlorine-based Kagomé layers which are intercalated with zigzag HCl chains in H4Cl7. These findings could help to understand how varied bonding features can co-exist and evolve in one compound under extreme conditions.
authors.affiliation: Science and Technology on Thermostructural Composite Materials Laboratory, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China. qfzeng@nwpu.edu.cn and International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China.
authors.forename: Qingfeng
authors.initials: Q
authors.lastname: Zeng
authors.affiliation: Science and Technology on Thermostructural Composite Materials Laboratory, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China. qfzeng@nwpu.edu.cn and International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China.
authors.forename: Shuyin
authors.identifier: http://orcid.org/0000-0001-6848-1531
authors.initials: S
authors.lastname: Yu
authors.affiliation: Science and Technology on Thermostructural Composite Materials Laboratory, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China. qfzeng@nwpu.edu.cn and International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China.
authors.forename: Duan
authors.initials: D
authors.lastname: Li
authors.affiliation: International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China and Department of Geosciences, Center for Materials by Design, and Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794-2100, USA and Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region 141700, Russia.
authors.forename: Artem R
authors.initials: AR
authors.lastname: Oganov
authors.affiliation: IC2MP UMR 7285, Université de Poitiers, CNRS, 4, rue Michel Brunet, TSA 51106, 86073 Poitiers Cedex 9, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Frapper