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Science 1 January 1999:
Vol. 283. no. 5398, pp. 44 - 46
DOI: 10.1126/science.283.5398.44
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Reports

Superionic and Metallic States of Water and Ammonia at Giant Planet Conditions

C. Cavazzoni, G. L. Chiarotti, * S. Scandolo, E. Tosatti, M. Bernasconi, M. Parrinello

The phase diagrams of water and ammonia were determined by constant pressure ab initio molecular dynamic simulations at pressures (30 to 300 gigapascal) and temperatures (300 to 7000 kelvin) of relevance for the middle ice layers of the giant planets Neptune and Uranus. Along the planetary isentrope water and ammonia behave as fully dissociated ionic, electronically insulating fluid phases, which turn metallic at temperatures exceeding 7000 kelvin for water and 5500 kelvin for ammonia. At lower temperatures, the phase diagrams of water and ammonia exhibit a superionic solid phase between the solid and the ionic liquid. These simulations improve our understanding of the properties of the middle ice layers of Neptune and Uranus.

C. Cavazzoni, G. L. Chiarotti, S. Scandolo, Istituto Nazionale per la Fisica della Materia (INFM) and International School for Advanced Studies (SISSA), Via Beirut 4, I-34014 Trieste, Italy. E. Tosatti, INFM and SISSA, Via Beirut 4, I-34014 Trieste, Italy, and International Centre for Theoretical Physics (ICTP), I-34014 Trieste, Italy. M. Bernasconi, INFM, and Dipartimento di Scienza dei Materiali, Universitá di Milano, Via Emanueli 15, I-20126 Milan, Italy. M. Parrinello, Max-Planck- Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany.
*   To whom correspondence should be addressed. E-mail: guido{at}sissa.it

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