Crystallization of Liquid Water in a Molecular Dynamics Simulation (original) (raw)
Related papers
Molecular dynamics simulations of ice growth from supercooled water
Molecular Physics, 2005
TIP4P/2005 force-field based classical molecular dynamics simulations were employed to investigate the microscopic mechanism for the ice growth from supercooled water when the external electric (0 − 10 9 V/m) and magnetic fields (0 − 10 Tesla) are applied simultaneously. Using the direct coexistence ice/water interface, the anisotropic effect of electric and magnetic fields on the basal, primary prismatic, and the secondary prismatic planes of ice Ih has been calculated. It was revealed for the first time that the solvation shells of supercooled water could be affected by the cooperative electric and magnetic fields. Meanwhile, the self diffusion coefficient is lowered and the shear viscosity increases considerably. The critical electric and magnetic fields to accelerate ice growth on the prismatic plane are fairly low (ca. 10 6 V/m and 0.01 Tesla). In contrast, the basal plane is hardly affected unless the fields increase to the order 10 9 V/m and 10 Tesla. Rotational dynamics of water molecules might play an important role in ice growth with the applied external fields. Density functional theory with the triple numerical all-electron basis set was used to reveal the electronic structures of the basal and primary prismatic planes of ice Ih with respect to the anisotropic effect of ice growth.
Molecular dynamics simulation of ice growth from supercooled pure water and from salt solution
Annals of Glaciology, 2006
The kinetics of ice growth on the prismatic and basal planes is studied by molecular dynamics simulations. The time evolution of two systems has been investigated. In one a slab of ice is initially in contact with supercooled water, while in the second the ice is in contact with a supercooled salt solution. The simulations were done at a temperature below the eutectic temperature, and complete solidification is observed. The total freezing time is longer in the systems with ions than in the systems with pure water. The final state for the salt systems always shows the formation of ion clusters. For the ionic system growing on the prismatic plane, an intermediate metastable state is observed before total solidification. The duration of this metastable state depends on the ability of the system to get all the ions participating in cluster formation. The simulations enable understanding of the mechanisms for ice formation under different solution conditions.
The Journal of Chemical Physics, 2011
The electric field dependence of the structure and dynamics of water at 77 K, i.e., below the glass transition temperature (136 K), is investigated using molecular dynamics simulations. Transitions are found at two critical field strengths, denoted \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}_{1}$\end{document}E1 and \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}_{2}$\end{document}E2. The transition around \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}_{1}\approx 3.5$\end{document}E1≈3.5 V/nm is characterized by the onset of significant structural disorder, a rapid increase in the orientational polarization, and a maximum in the dynamical fluctuations. At \documentclass[12pt]{minimal}\begin{document}$\mathcal {E}_{2}\approx 40$\end{document}E2≈40 V/nm, the system crystallizes in discrete steps into a body-centered-cubic unit cell that minimizes the potential energy by simultaneous superpolarization of the water molecular dipoles and maximization...
Structural and dynamical properties of nanoconfined supercooled water
2011
Bulk water presents a large number of crystalline and amorphous ices. Hydrophobic nanoconfinement is known to affect the tendency of water to form ice and to reduce the melting temperature. However, a systematic study of the ice phases in nanoconfinement is hampered by the computational cost of simulations at very low temperatures. Here we develop a coarse-grained model for a water monolayer in hydrophobic nanoconfinement and study the formation of ice by Mote Carlo simulations. We find two ice phases: low-density-crystal ice at low pressure and high-density hexatic ice at high pressure, an intermediate phase between liquid and high-density-crystal ice.
2009
Molecular dynamics simulations of ice I h in a slab geometry with a free basal (0001) surface are carried out at 250 K in order to study the structure and dynamics of the ice/vapor interface, focusing on processes associated with sublimation and deposition. Surface melting, which results in the formation of a quasi-liquid layer, causes about 8% of the molecules originally constituting the surface bilayer to leave their crystal lattice positions and form an outer, highly mobile sublayer. Molecules in this sublayer typically form two H-bonds, predominantly in a dangling-O orientation, with preference for a dangling-H orientation also evident. The remaining 92% of the quasi-liquid layer molecules belong to the deeper, more crystalline sublayer, typically forming three H-bonds in an orientational distribution that closely resembles bulk crystalline ice. Transitions between the quasi-liquid layer and the first underlying crystalline bilayer were also observed on the molecular dynamics simulation time scale, albeit with substantially longer characteristic times. Regarding deposition, a very high (>99%) probability of water vapor molecules sticking to the ice surface was found. 70% of incident molecules adsorb to the outer sublayer, while 30% are accommodated directly to the inner sublayer of the quasi-liquid layer, with an orientational relaxation time of ~2 picoseconds and a thermal relaxation time of ~10 picoseconds. Regarding the mechanism of sublimation, we found that prior to sublimation, departing molecules are predominantly located in the outermost sublayer and show a distinct preference for a dangling-O orientation.
Simulations of liquid crystals: bulk structure and interfacial properties
2001
We present large scale molecular dynamics simulations of liquid crystals, which are modeled as fluids of soft repulsive ellipsoidal molecules. In the first part of the paper, we discuss the bulk structure of nematic liquid crystals. The direct correlation function (DCF) has been determined for the first time in a nematic fluid without any approximations. We demonstrate that it can be used to calculate the Frank elastic constants, which are important phenomenological parameters in the continuum theory of liquid crystals.
Molecular dynamics simulation of crystal water with X-ray constraints
International Journal of Quantum Chemistry, 1994
The study of water in macromolecular crystals is approached with a restrained molecular dynamics method that makes use of X-ray diffraction data, without the need of thermal B factors for the solvent. This method, called here solute-grid-restrained molecular dynamics (SGRMD), is applied to a test case of a simulated crystal of erythrol. The results are quite satisfactory, and it is concluded that the method can be useful to study real macromolecular crystals. © 1994 John Wiley & Sons, Inc.
Micro-Electro-Mechanical Systems (MEMS), 1997
Recent experiments have found that hexadecyl-trimethyl-ammonium bromide (CTAB) to have superior ice nucleation inhibition properties [J. Phys. Chem. B 121, 6580]. The mechanism on how the inhibition takes place remains unclear. Therefore, molecular dynamics was used to simulate ice crystallization of a water/CTAB/ice system. The ice crystallization rate for a pure water system was compared for the basal [0001], first prism [10-10], and secondary prism plane [11-20], where the basal plane grew the slowest followed by the first prism plane. When CTAB was added to the ice-liquid water system, crystallization was clearly impeded. Even when ice starts growing away from the CTAB molecule, the hydrophilic head would at some point protrude and get caught in the water/ice interface. Once the head of the CTAB was encapsulated in the advancing interface, the hydrophobic body would wriggle around and disrupt the formation of hydrogen bond networks that are essential for ice growth. When the interface clears the length of the body of the CTAB molecule, ice crystallization resumes at its normal pace. In summary, the inhibition of ice growth is a combination of the hydrophilic head acting as an anchor and the dynamic motion of the hydrophobic tail hindering stable hydrogen bonding for ice growth.
Thermodynamic and Structural Aspects of the Potential Energy Surface of Simulated Water
Relations between the thermodynamics and dynamics of supercooled liquids approaching a glass transition is a topic of considerable interest. The potential energy surface of model liquids has been increasingly studied, since it provides a connection between the configurational component of the partition function on the one hand, and the system dynamics on the other. This connection is most obvious at low temperatures, where the motion of the system can be partitioned into vibrations within a basin of attraction and infrequent interbasin transitions. In this work, we present a description of the potential energy surface properties of supercooled liquid water. The dynamics of this model have been studied in great detail in recent years. We locate the minima sampled by the liquid by ''quenches'' from equilibrium configurations generated via molecular dynamics simulations, and then calculate the temperature and density dependence of the basin energy, degeneracy, and shape. The temperature dependence of the energy of the minima is qualitatively similar to simple liquids, but has anomalous density dependence. The unusual density dependence is also reflected in the configurational entropy, the thermodynamic measure of degeneracy. Finally, we study the structure of simulated water at the minima, which provides insight on the progressive tetrahedral ordering of the liquid on cooling.