A new phase diagram of water under negative pressure: The rise of the lowest-density clathrate s-III

Authors

Yingying Huang, Dalian University of Technology
Chongqin Zhu, University of Nebraska-Lincoln
Lu Wang, University of Science and Technology of China
Xiaoxiao Cao, Dalian University of Technology
Yan Su, Dalian University of Technology
Xue Jiang, Dalian University of Technology
Sheng Meng, Chinese Academy of Sciences
Jijun Zhao, Dalian University of TechnologyFollow
Xiao Cheng Zeng, University of Nebraska-LincolnFollow

Date of this Version

2-12-2016

Citation

Y. Huang, C. Zhu, L. Wang, X. Cao, Y. Su, X. Jiang, S. Meng, J. Zhao, X. C. Zeng, A new phase diagram of water under negative pressure: The rise of the lowest-density clathrate s-III. Sci. Adv. 2, e1501010 (2016).

Comments

Copyright © 2016 The Authors. Used by permission.

Abstract

Ice and ice clathrate are not only omnipresent across polar regions of Earth or under terrestrial oceans but also ubiquitous in the solar system such as on comets, asteroids, or icy moons of the giant planets. Depending on the surrounding environment (temperature and pressure), ice alone exhibits an exceptionally rich and complicated phase diagram with 17 known crystalline polymorphs.Water molecules also form clathrate compounds with inclusion of guest molecules, such as cubic structure I (s-I), cubic structure II (s-II), hexagonal structure H (s-H), tetragonal structure T (s-T), and tetragonal structure K (s-K). Recently, guest-free clathrate structure II (s-II), also known as ice XVI located in the negative-pressure region of the phase diagram of water, is synthesized in the laboratory and motivates scientists to reexamine other ice clathrates with low density. Using extensive Monte Carlo packing algorithm and dispersion-corrected density functional theory optimization, we predict a crystalline clathrate of cubic structure III (s-III) composed of two large icosihexahedral cavities (8⁶6⁸4¹²) and six small decahedral cavities (8²4⁸) per unit cell, which is dynamically stable by itself and can be fully stabilized by encapsulating an appropriate guest molecule in the large cavity. A new phase diagram of water ice with TIP4P/2005 (four-point transferable intermolecular potential/2005) model potential is constructed by considering a variety of candidate phases. The guest-free s-III clathrate with ultralow density overtakes s-II and s-H phases and emerges as the most stable ice polymorph in the pressure region below −5834 bar at 0 K and below −3411 bar at 300 K.