title: Crystal structures and dynamical properties of dense CO2.
abstract: Structural polymorphism in dense carbon dioxide (CO2) has attracted significant attention in high-pressure physics and chemistry for the past two decades. Here, we have performed high-pressure experiments and first-principles theoretical calculations to investigate the stability, structure, and dynamical properties of dense CO2We found evidence that CO2-V with the 4-coordinated extended structure can be quenched to ambient pressure below 200 K-the melting temperature of CO2-I. CO2-V is a fully coordinated structure formed from a molecular solid at high pressure and recovered at ambient pressure. Apart from confirming the metastability of CO2-V (I-42d) at ambient pressure at low temperature, results of ab initio molecular dynamics and metadynamics (MD) simulations provided insights into the transformation processes and structural relationship from the molecular to the extended phases. In addition, the simulation also predicted a phase V'(Pna21) in the stability region of CO2-V with a diffraction pattern similar to that previously assigned to the CO2-V (P212121) structure. Both CO2-V and -V' are predicted to be recoverable and hard with a Vicker hardness of ∼20 GPa. Significantly, MD simulations found that the CO2in phase IV exhibits large-amplitude bending motions at finite temperatures and high pressures. This finding helps to explain the discrepancy between earlier predicted static structures and experiments. MD simulations clearly indicate temperature effects are critical to understanding the high-pressure behaviors of dense CO2structures-highlighting the significance of chemical kinetics associated with the transformations.
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada S7N 5E2.
authors.forename: Xue
authors.initials: X
authors.lastname: Yong
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada S7N 5E2; hanyuliu801@gmail.com John.Tse@usask.ca csyoo@wsu.edu.
authors.forename: Hanyu
authors.initials: H
authors.lastname: Liu
authors.affiliation: College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou, 310014, People's Republic of China.
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada S7N 5E2.
authors.forename: Yansun
authors.initials: Y
authors.lastname: Yao
authors.affiliation: Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Canada S7N 5E2; hanyuliu801@gmail.com John.Tse@usask.ca csyoo@wsu.edu.
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.affiliation: Department of Chemistry, Washington State University, Pullman, WA 99164-2816.
authors.forename: Ranga
authors.initials: R
authors.lastname: Dias
authors.affiliation: Department of Chemistry, Washington State University, Pullman, WA 99164-2816 hanyuliu801@gmail.com John.Tse@usask.ca csyoo@wsu.edu.
authors.forename: Choong-Shik
authors.initials: CS
authors.lastname: Yoo
keywords: carbon dioxide; high pressure; material science; molecular dynamics