Molecular dynamics simulations of ice growth from supercooled water (original) (raw)
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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.
We present a first-principles study of the properties of ordinary hexagonal ice (phase I h ) and of its proton-ordered version (phase XI) under the action of static electric fields. We compute the mechanical response to the field in addition to the ionic current-voltage diagrams; we also analyze several other microscopic aspects of the proton transfer mechanism, with particular emphasis on the role played by the oxygen sublattice in driving molecular dissociation. We further study the topological aspects of the mechanical and electrical responses by orienting the external field along two different crystalline directions in both ice samples. At variance with ice I h , ice XI displays an anisotropic behavior in the range of explored field intensities. In fact, when the direction of the field coincides with the ferroelectric axis, sustained molecular dissociation and proton transfer events are both observed just beyond a given field intensity; instead, the two processes exhibit different activation thresholds when the field is oriented along another symmetry axis. The underlying mechanism of molecular dissociation appears to be the same in solid and liquid water independently of the direction of the field.
The journal of physical chemistry. B, 2014
We present a first-principles study of the properties of ordinary hexagonal ice (phase I(h)) and of its proton-ordered version (phase XI) under the action of static electric fields. We compute the mechanical response to the field in addition to the ionic current-voltage diagrams; we also analyze several other microscopic aspects of the proton transfer mechanism, with particular emphasis on the role played by the oxygen sublattice in driving molecular dissociation. We further study the topological aspects of the mechanical and electrical responses by orienting the external field along two different crystalline directions in both ice samples. At variance with ice Ih, ice XI displays an anisotropic behavior in the range of explored field intensities. In fact, when the direction of the field coincides with the ferroelectric axis, sustained molecular dissociation and proton transfer events are both observed just beyond a given field intensity; instead, the two processes exhibit different...
Structure order, local potentials, and physical anomalies of water ice
arXiv (Cornell University), 2014
This treatise deals with the structure order, local potentials, and physical anomalies demonstrated by water ice under compression, coordination number reduction, and thermal excitation. A "master-slave segmented H-bond (O:H-O)" forms a pair of asymmetric, H-bridged, coupled oscillators with short-range interactions and memory. This notation allows for specification of forces driving its cooperative relaxation. The cooperativity of the H-bond in length and energy and the associated binding electron entrapment and nonbonding electron polarization dictate the unusual performance of water ice. It has been revealed that: i) Compression shortens-and-stiffens the softer "O:H" bond and lengthens-and-softens the stiffer "H-O" covalent bond through repulsion between electron-pair on adjacent oxygen atoms, yielding the low compressibility, proton symmetrization, phase-transition temperature (T C) depression, softer phonon (< 300 cm-1) stiffening and stiffer phonon (> 3000 cm-1) softening; ii) Driven by the spontaneous H-O covalent bond contraction, molecular-undercoordination effects oppositely to compression. This process results in a supersolid phase that undergoes molecular size contraction and separation expansion, melting point (viscosity) elevation, binding energy entrapment, bonding charge densification, nonbonding lone electron polarization, stiffer phonon stiffening and softer phonon softening. The supersolidity of molecule clusters, surface skins, and ultrathin films of water makes them perform like ice and hydrophobic at the ambient temperature and frictionless of ice; iii) The disparity of the segmental specific heat discriminates the O:H from the H-O in responding to cooling, which shortens alternatively the segments in liquid, liquid-solid transition, solid, and ice at T < 80 K, resulting in four-region density and phonon-stiffness oscillation. The basic rule of sp 3-orbital hybridization of oxygen, detectable density, and the segmental length cooperativity have enabled a solution to discrepancies on the size, separation, structural order, and mass density of molecules packing in water and ice. It is emphasized that focusing on the statistical mean of all the cooperative parameters is more reliably revealing than on the instantaneous accuracy of one parameter at a time for the strongly correlated and fluctuating system of liquid water. Reconciling observations of O:H and H-O length symmetry under compression, O-O separation change at a surface and at cooling, solution clarifies: i) the preference of the fluctuated tetragonal structure of water, ii) the essence of inter electron-pair repulsion, and iii) the presence of the supersolid phase at regions consisting molecules with fewer than four neighbors. A combination of the Lagrangian vibration mechanics, molecular dynamics decomposition of volume evolution, and Raman spectroscopy of phonon relaxation has enabled probing of the asymmetric, local, short-range potentials pertaining to the O:H-O bond. Coulomb mediation of the intermolecular interaction results in the Hofmeister effect. Numerical solution to the Fourier equation for the fluid thermodynamics with the skin supersolidity resolved the Mpemba paradox that happens only in the non-adiabatic ambient. O:H-O bond has a memory to emit heat at a rate depending on the initial energy storage and the skin supersolidity creates the gradients of density, specific heat, and thermal conductivity. The memory of O:H-O bond may have implication to the signaling, messaging, and self-recovery of damage for living cells.
Electric fields in ice and near water clusters
The Journal of Chemical Physics, 2000
We have studied the electric field near water clusters and in ice Ih using first principles calculations. We employed Mo "ller-Plesset perturbation theory ͑MP2͒ for the calculations of the clusters up to and including the hexamer, and density functional theory ͑DFT͒ with a gradient dependent functional ͓Perdew-Wang ͑PW91͔͒ for ice Ih as well as the clusters. The electric field obtained from the first principles calculations was used to test the predictions of an induction model based on single center multipole moments and polarizabilities of an isolated water molecule. We found that the fields obtained from the induction model agree well with the first principles results when the multipole expansion is carried out up to and including the hexadecapole moment, and when polarizable dipole and quadrupole moments are included. This implies that accurate empirical water interaction potential functions transferable to various environments such as water clusters and ice surfaces could be based on a single center multipole expansion carried out up to the hexadecapole. Since point charges are not included, the computationally intensive Ewald summations can be avoided. Molecular multipole moments were also extracted from the first principles charge density using zero flux dividing surfaces as proposed by Bader. Although the values of the various molecular multipoles obtained with this method are quite different from the ones resulting from the induction model, the rate of convergence of the electric field is, nevertheless, quite similar.
Influence of dipole interaction on lattice dynamics of crystalline ice
2005
The Born effective charges of component atoms and phonon spectra of a tetrahedrally coordinated crystalline ice are calculated from the first principles method based on density functional theory within the generalized gradient approximation with the projected augmented wave method. Phonon dispersion relations in a 3× 1× 1 supercell were evaluated from Hellmann-Feynman forces with the direct method. This calculation is an additional work to the direct method in calculating the phonon spectra which does not take into account the polarization charges arising from dipole interaction of molecules of water in ice. The calculated Born effective polarization charges from linear response theory are supplied as the correction terms to the dynamical matrix in order to further investigate the LO-TO splitting of the polar modes of ice crystal at k = 0 which has long been speculated for this system especially in the region between 28 and 37 meV both in the theoretical and experimental studies. Our results clearly show the evidence of splitting of longitudinal and transverse optic modes at the k = 0-point in agreement with some experimental findings.
Molecular multipole moments of water molecules in ice Ih
Chemical Physics, 1998
We have used an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments to study the electric field in ice. The self-consistent induction calculations gave an average total dipole moment of 3.09 D, a 67% increase over the dipole moment of an isolated water molecule. A previous, more approximate induction model study by Coulson and Eisenberg [Proc. R. Soc. Lond. A 291, 445 (1966)] suggested a significantly smaller average value of 2.6 D. This value has been used extensively in recent years as a reference point in the development of various polarizable interaction potentials for water as well as for assessment of the convergence of water cluster properties to those of bulk. The reason for this difference is not due to approximations made in the computational scheme of Coulson and Eisenberg but rather due to the use of less accurate values for the molecular multipoles in these earlier calculations.
Ab initio study of the structure and dynamical properties of crystalline ice
Phase Transitions, 2005
We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3x1x1 supercell by using the direct method. So far, due to the direct method used in this calculation, the phonon spectra is obtained without taking into account the effect of polarization arising from dipole-dipole interactions of water molecules which is expected to yield the splitting of longitudinal and transverse optic modes at the Gamma-point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode is in a reasonable agreement with the neutron scatering data. The analysis of the vibrational density of states shows the existence of a boson peak at low energy of translational region a characteristic common to amorphous systems.