期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 106, 期 15, 页码 6077-6081出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0812624106
关键词
solid CO2; first-principles molecular dynamics; metadynamics; phase transition; density functional theory
资金
- Natural Sciences and Engineering Research Council
- Alexander von Humboldt fellowship
- PRIN-Cofin [2006022847]
- EUROCORES EuroSlab
- Consiglio Nazionale delle Ricerche/Istituto Nazionale di Fisica della Materia
- SISSA/Central European Initiative Grant
- High Performance Computing-Europa through Consorzio Interuniversitario CINECA [VEGA 1/0096/08, APVV-0442-07, VVCE-0058-07]
- Centre of Excellence of the Slovak Academy of Sciences
Understanding the structural transformations of solid CO2 from a molecular solid characterized by weak intermolecular bonding to a 3-dimensional network solid at high pressure has challenged researchers for the past decade. We employ the recently developed metadynamics method combined with ab initio calculations to provide fundamental insight into recent experimental reports on carbon dioxide in the 60-80 GPa pressure region. Pressure-induced polymeric phases and their transformation mechanisms are found. Metadynamics simulations starting from the CO2-II (P4(2)/mnm) at 60 GPa and 600 K proceed via an intermediate, partially polymerized phase, and finally yield a fully tetrahedral, layered structure (P-4m2). Based on the agreement between calculated and experimental Raman and X-ray patterns, the recently identified phase VI [Iota V, et al. (2007) Sixfold coordinated carbon dioxide VI. Nature Mat 6: 34-38], assumed to be disordered stishovite-like, is instead interpreted as the result of an incomplete transformation of the molecular phase into a final layered structure. In addition, an alpha-cristobalite-like structure (P4(1)2(1)2), is predicted to be formed from CO2-III (Cmca) via an intermediate Pbca structure at 80 GPa and low temperatures (< 300 K). Defects in the crystals are frequently observed in the calculations at 300 K whereas at 500 to 700 K, CO2-III transforms to an amorphous form, consistent with experiment [Santoro M, et al. (2006) Amorphous silica-like carbon dioxide. Nature 441: 857-860], but the simulation yields additional structural details for this disordered solid.
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