Crystallization of Liquid Water in a Molecular Dynamics Simulation

Abstract

In this Letter we report our success in crystallizing a bulk sample of liquid water in molecular dynamics simulations.In these computer experiments supercooled liquid TIP4P water at 250 K was subjected to a homogeneous static electric field; the resulting polar crystal which forms within 200 ps has the structure of ice I,. These simulation results suggest that the local electric fields that exist near the surfaces of various materials or within confined geometries can play an important role in promoting the crystallization of liquid water. PACS numbers: 61.25.Em, 64.60.Qb, 64.70.Dv Although the structure and physical properties of liquid water at room temperature [1 -3] are now well established, a fundamental understanding of its lowtemperature behavior [4 -6] is still lacking. Upon freezing, water can form various crystalline and amorphous ices [2, 4 -6]. Under certain conditions these solids exhibit a complex series of phase transformations [4 -8] which, together with the thermodynamic anomalies of the supercooled liquid [4,6], remain the subject of intense debate. In recent years computer simulations have contributed greatly to this area. Among many such studies [6,8 -13] the enormous computational efforts undertaken by Poole, Sciortino, Essmann, and Stanley [6,8] to model metastable phases of solid water are of particular note. In their work they have used molecular dynamics (MD) simulations to help construct a phase diagram for low-and high-density amorphous ice. However, despite these tremendous computational efforts, no one had yet succeeded in crystallizing a bulk sample of water in a computer simulation.We are aware of no simulation study in which any isotropic molecular liquid was continuously transformed into a regular solid. It is not surprising then that freezing phenomena [14],although among the most fundamental in nature, still remain rather poorly understood at the microscopic level.Thermodynamics views the transformation of a molecular liquid into a molecular crystal as a first-order phase transition. In the absence of a foreign surface or particle to promote heterogeneous nucleation, this phase transition begins with the spontaneous nucleation of molecules into small aggregates which, if they reach a critical size, form the seeds for the new phase. Unfortunately, computer simulation methods have been unable to model this dynamical process directly, the large-scale density and polarization fluctuations that might initiate formation of a heterophase have not been recorded even for very large systems. Upon reducing the temperature, phase trajectories tend to get trapped into a region of rnetastable glassy states [6] which makes it impossible to follow further the evolution of a molecular system towards its crystalline state.We have attempted to bypass these limitations by applying a static electric field in MD simulations of TIP4P [15] water and have discovered that the deeply supercooled liquid can be completely transformed into a polar crystal with the regular structure of ice I within only a f...

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

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Molecular Dynamics Simulations of Water with Novel Shell-Model Potentials

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Translational dynamics of a cold water cluster in the presence of an external uniform electric field

“…Recently, it was possible to produce ice cubic structures in molecular dynamics ͑MD͒ simulations [2][3][4][5][6][7][8][9][10][11][12][13] by applying a rather strong electric field on supercooled liquid water. Although this transformation in bulk water and in Stockmayer fluids 14,15 has been studied in some detail, mainly from the structural point of view, the precise route to crystallization with increasing field strength and the concomitant change in dynamics has not been given equal attention.…”