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A New Phase Diagram of Water Under Negative Pressure: the Rise of the Lowest-Density Clathrate S- III Yingying Huang Dalian University of Technology

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A New Phase Diagram of Water Under Negative Pressure: the Rise of the Lowest-Density Clathrate S- III Yingying Huang Dalian University of Technology University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Xiao Cheng Zeng Publications Published Research - Department of Chemistry 2-12-2016 A new phase diagram of water under negative pressure: The rise of the lowest-density clathrate s- III 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 See next page for additional authors Follow this and additional works at: http://digitalcommons.unl.edu/chemzeng Huang, Yingying; Zhu, Chongqin; Wang, Lu; Cao, Xiaoxiao; Su, Yan; Jiang, Xue; Meng, Sheng; Zhao, Jijun; and Zeng, Xiao Cheng, "A new phase diagram of water under negative pressure: The rise of the lowest-density clathrate s-III" (2016). Xiao Cheng Zeng Publications. 122. http://digitalcommons.unl.edu/chemzeng/122 This Article is brought to you for free and open access by the Published Research - Department of Chemistry at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Xiao Cheng Zeng Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Yingying Huang, Chongqin Zhu, Lu Wang, Xiaoxiao Cao, Yan Su, Xue Jiang, Sheng Meng, Jijun Zhao, and Xiao Cheng Zeng This article is available at DigitalCommons@University of Nebraska - Lincoln: http://digitalcommons.unl.edu/chemzeng/122 RESEARCH ARTICLE WATER CHEMISTRY 2016 © The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed A new phase diagram of water under negative under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). pressure: The rise of the lowest-density 10.1126/sciadv.1501010 clathrate s-III Yingying Huang,1,2* Chongqin Zhu,2,3* Lu Wang,4 Xiaoxiao Cao,1 Yan Su,1 Xue Jiang,1 Sheng Meng,3 Jijun Zhao,1† Xiao Cheng Zeng2,4† 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 struc- ture 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. INTRODUCTION thegashydrateoriceclathrate(15–18). In the ice clathrates, water Water molecules are the third most abundant molecular species in molecules form loosely hydrogen-bonded framework connected by in- the universe (1). Ice, the form of water in condensed state, is the most terlinked cages whose inner cavities are either completely or partially common molecular solid on Earth and can be also detected in the occupied by guest molecules. So far, at least five types of ice clathrate giant planetary interior. The existence of water and ice has implication structures have been experimentally identified (11, 15, 19)ortheoret- to the diversity of nature and possible presence of life. Because of the ically proposed (20), namely, cubic structure I (s-I) with 2 512 cages flexible hydrogen bonds, water ice exhibits an exceptionally rich and and 6 51262 cages per unit cell; cubic structure II (s-II) with 16 512 complicated phase diagram (2–10). Under different conditions of cages and 8 51264 cages; hexagonal structure H (s-H) with 3 512 cages, pressure (P)andtemperature(T), there are 17 experimentally estab- 2435663 cages, and 1 51268 cage; tetragonal structure T (s-T) with 2 lished crystalline phases of ice so far (2, 3, 11). Among them, ice XI 425864 cages; and tetragonal structure K (s-K) with 6 512 cages, 4 51263 has the lowest mass density of 0.930 g/cm3 and forms a proton- cages, and 4 51262 cages per unit cell, respectively. Usually, the clathrate ordered phase at zero temperature and ambient pressure (12). At hydrates are considered as hypothetical phases of water (21, 22)and elevated temperature (72 K), ice XI transforms into a proton-disordered have to be stabilized by favorable van der Waals (vdW) interactions phase, that is, the well-known ice Ih (12). In addition, many hypo- between guest molecules and host water cages (16–18, 23). However, thetical ice phases are also predicted and wait experimental confir- Falenty and co-workers (11) recently synthesized guest-free s-II mation, for example, virtual ices i and i′ with low density (13), ice 0 clathrate (also named ice XVI) by leaching Ne atoms from the s-II as a precursor to ice nucleation (5), silica-like ice polymorphs (14), Ne clathrate. The guest-free s-II clathrate is mechanically stable at and partially ionic phase of water ice under extremely high pressure atmospheric pressure up to a temperature of 145 K and exhibits neg- (5 to 50 Mbar) (6–10). ative thermal expansion with good mechanical stability and larger Apart from pure water ices, water and various gas molecules (such lattice constants than the filled clathrate. The experimental realiza- as Ne, Ar, H2,CO2,CH4,C2H6, adamantane, and methylcyclohexane) tion of empty s-II lattice not only confirms that water molecules can form a class of nonstoichiometric inclusion compounds, namely, themselves can form loose crystalline phase with density lower than ice XI but also motivates us to further explore other possible low- 1Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian density polymorphs of water ice that are stable at low temperatures University of Technology, Ministry of Education, Dalian 116024, China. 2Department of and negative pressures. Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska, In contrast to the comprehensive knowledge of phase diagram of Lincoln, NE 68588, USA. 3Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. 4Hefei water under positive pressures, the negative-pressure region of the National Laboratory for Physical Sciences at the Microscale and Collaborative diagram is much less explored (21, 22, 24, 25). Some efforts have Innovation Center of Chemistry for Energy Materials, Department of Materials Science been devoted to determining the limiting mechanical tension that and Engineering, University of Science and Technology of China, Hefei 230026, China. *These authors contribute equally to this work. the stretched liquid water can sustain before the event of nucleation †Corresponding author. E-mail: [email protected] (J.Z.); [email protected] (X.C.Z.) occurs, namely, the cavitation pressure (24–28). Classical nucleation Huang et al. Sci. Adv. 2016; 2 :e1501010 12 February 2016 1of6 RESEARCH ARTICLE theory predicted a cavitation pressure of about −1900 bar for water the guest-free s-III unit cell. The fractional coordinates of the s-III at room temperature (25, 26). A large negative pressure of about −1400 bar clathrate are given in table S1. Real-space force constants of the in the microscopic aqueous inclusions inside a quartz matrix was re- guest-free s-III clathrate were calculated by using the density function- ported (27). A negative pressure of −1600 bar in water capillary bridges al perturbation theory as implemented in Vienna Ab initio Simulation was also measured with an atomic force microscope (28). Package (VASP). The phonon dispersion was then computed from Besides the stretched liquid water, guest-free clathrates can be re- the real-space force constants using the Phonopy package (32) (see garded as low-density phases of water ice that exist in the negative- fig. S1). No imaginary frequency is found within the entire Brillouin pressure region of the phase diagram (21, 22, 29, 30) and have been zone, confirming its dynamic stability. investigated by classical molecular dynamics (MD) simulations. To investigate the competition of different low-density ice poly- Jacobson et al.(29) established a P-T phase diagram with inclusion morphs, here we took ice XI (12) as reference and considered a num- of liquid water, ice Ih, and s-I and s-II clathrates and concluded that ber of guest-free ice clathrates, that is, s-I, s-II, s-H (19), s-K (20), SGT guest-free s-II clathrate is the stable phase of water at P ≤−1320 bar (sigma-2) as a silica analog (33), s-T (15),ands-III,aswellasvirtual and T ≤ 275 K. Using TIP4P/2005 (four-point transferable intermolecular ice i (13) for comparison, which are displayed in fig. S2. Their equi- potential/2005) model (31), Conde et al.(21) found that the sequence librium volume of unit cell, average O-O distance, mass density, and of stable phases of water at negative pressure is ice XI, s-II, and s-H clath- lattice cohesive energy from DFT calculations are summarized in Table rates.
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