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Fracture in ice Ih is simulated with molecular dynamics utilizing two potential fields, TIP4P/Ice and mW, and in different temperature conditions. The simulations produce propagating crack speeds over a large range of fracture energies. Terminal crack speed simulated with TIP4P/Ice potential can reach more than 200 m/s befitting experimental results. On the other hand, for mW potential, crack speed is around 5 m/s. The TIP4P/ice model suggests a brittle ice while mW potential describes a much more ductile material. The computational simulations are designed to permit direct comparison with experiments which can be performed in the hereafter. This comparison could provide a sensitive test to interatomic potentials. [ABSTRACT FROM AUTHOR]

Due to their great importance in science, technology, and the life sciences, water and ice have been extensively investigated over many years. In particular, hexagonal ice Ih has been of great interest since it is the most common form of ice, and several modifications, Ih(a), Ih(b) and Ih(c) are known, whose structural details are still under discussion. In this study, we present an alternative theoretical model, called Ih(d), for the hexagonal ice modification in space group P63/mmc (no. 194), based on first-principles calculations that have been performed using DFT-LDA, GGA-PBE, and hybrid B3LYP and PBE0 functionals. [ABSTRACT FROM AUTHOR]

Highlights • The Cartesian components of the partial vibrational density of states (p VDOS) of the protons and oxygen atom in light ice (Ih) are simulated for the first time by first principle modeling based on density functional theory (DFT). • The directional p VDOS are utilized for calculating the Cartesian components of the atomic kinetic energies, Ke(H) and Ke(O), along and perpendicular to the hydrogen bonds (HBs) in light ice (Ih). • The DFT method is found to yield better agreement with deep inelastic neutron scattering (DINS) measurements compared to semi empirical calculations. • The kinetic energy fractions shared by the proton in each mode of motion of H2O along and normal to the HBs in ice Ih are also resolved for the first time. • The present study emphasizes the potential of a p VDOS analysis as a powerful theoretical tool for studying nuclear energies, and in particular, resolving possible competing (CQEs) and nuclear (NQEs) quantum effects in HBs containing systems, e.g. as in ordinary H2O phases and in nanoconfined water. Abstract The partial vibrational density of states (p VDOS) of ice Ih, as simulated by first principle modeling based on density functional theory (DFT), is utilized for computing the Cartesian components of the proton and oxygen quantum kinetic energies, Ke(H) and Ke(O) respectively, along and perpendicular to the hydrogen bonds. The DFT method was found to yield better agreement with deep inelastic neutron scattering (DINS) measurements than the semi empirical (SE) calculations. The advantage of using the DFT method is to enable us to resolve the external and internal phonon bands of the Cartesian projections of the p VDOS, and hence those of the lattice and vibrational components of Ke(H). We show that a p VDOS analysis is a valuable tool in testing scattering results of complex systems and suggest its potential to explore competing quantum effects, e.g. on Ke(H) across phase transitions in water. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

We explore the links between strain localisation and microstructural evolution in ice Ih deformed by dislocation creep. Using digital image correlation (DIC), we monitored the evolution of the strain field in two coarse-grained columnar ice samples deformed by creep (uniaxial compression at constant load) at −7 °C and 0.5 MPa up to 9.5% bulk shortening. After a brief transient (<0.2% bulk strain), in which strain localises nearby grain boundaries, viscoplastic strain concentrates in a few narrow intracrystalline shear bands that eventually extend over multiple grains. A comparison of pre- and post-deformation crystal orientation maps shows that strain localisation in shear bands is mainly accommodated by basal slip without producing significant dislocation-related substructures. Severe dynamic recrystallisation develops locally at grain boundaries that act as barriers to dislocation motion, particularly where basal shear transfer is ineffective. These observations are compared to full-field simulations reproducing the initial microstructure and experimental setup, which predict the stress and strain rate fields for deformation entirely accommodated by dislocation slip on the known slip systems in ice. The present data indicate that during the deformation of coarse-grained ice Ih at high homologous temperatures: (1) recrystallisation does not drive strain localisation but accommodates strain incompatibility, and (2) large strains can be accommodated by unimpeded basal slip with no formation of dislocation substructures. Observation (2) implies that intragranular orientation gradients are unreliable gauges of viscoplastic strain intensity at the grain scale and that the proportion of dislocation types in subgrains does not measure the relative contribution of different slip systems to deformation. Finally, we discuss the implications of this study for the interpretation and modelling of deformation by dislocation creep in rocks. • Transient strain localisation at most grain boundaries occurs at strains <0.2%. • At higher strains, deformation occurs on a network of intracrystalline shear bands. • Shear bands associated with dislocation slip can leave no microstructural record. • Intragranular orientation gradients do not gauge strain intensity. • Recrystallisation mainly accommodates grain-scale strain incompatibility. [ABSTRACT FROM AUTHOR]

The polarized Raman spectra of the upper part of a thin ice I h film were obtained in the range of 150 cm−1 to 3800 cm−1. The spectra showed clear polarization dependence; several new peaks were also observed. The longitudinaloptic-tranverseoptic (LO-TO) splitting of the mode near 220 cm−1 in the translational vibration region was experimentally confirmed at 133 K. The Fermi resonance between the bending overtone (around 3270 cm−1) and symmetry stretching fundamental (around 3350 cm−1) in the stretching vibration region appeared at nearly the same temperature. Results showed that ice XI (i.e. proton-ordered phase of ice I h) slowly formed in the upper part of a thin ice I h film without KOH as the temperature gradually decreased below 133 K. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the present contribution we summarize our observations concerning the ultrafast non-equilibrium dynamics of water, in both the liquid and crystalline phase. Our experimental tool is two-dimensional infrared (2D IR) spectroscopy, which combines structural information on a molecular level with femtosecond time resolution. In the case of liquid and supercooled water we are able to extract the timescales of hydrogen bonding dynamics, whereas in the ice form we can probe the change of the hydrogen bond properties under excitation and observe the influence of intermolecular mode excitations in the crystal.

Abstract: From our recent research on ice Ih (hexagonal ice), we deduce that free OH groups exist at the ice surface and that dangling OH influences the interior of the proton-disordered ice. Additionally, exploiting recent research by others on water molecular clusters, we propose a new interpretation for the Raman OH stretching vibration of ice Ih. We deconvolute the Raman OH stretching vibration of ice Ih into four sub-bands, with each sub-band being ascribed to OH vibrations engaged in different types of hydrogen bonding. [Copyright &y& Elsevier]

Abstract: Wideband far infrared (FIR) spectra of complex permittivity ε(ν) of ice are calculated in terms of a simple analytical theory based on the method of dipolar autocorrelation functions. The molecular model represents a revision of the model recently presented for liquid water in Adv. Chem. Phys. 127 (2003) 65. A composite two-fractional model is proposed. The model is characterised by three phenomenological potential wells corresponding to the three FIR bands observed in ice. The first fraction comprises dipoles reorienting in a rather narrow and deep hat-like well; these dipoles generate the librational band centred at the frequency ≉880cm-1. The second fraction comprises elastically interacting particles; they generate two nearby bands placed around frequency 200cm-1. For description of one of these bands the harmonic oscillator (HO) model is used, in which translational oscillations of two charged molecules along the H-bond are considered. The other band is produced by the H-bond stretch, which governs hindered rotation of a rigid dipole. Such a motion and its dielectric response are described in terms of a new cut parabolic (CP) model applicable for any vibration amplitude. The composite hat-HO–CP model results in a smooth ε(ν) ice spectrum, which does not resemble the noise-like spectra of ice met in the known literature. The proposed theory satisfactorily agrees with the experimental ice spectrum measured at -7°C. The calculated longitudinal optic-transverse optic (LO–TO) splitting occurring at ≉250cm-1 qualitatively agrees with the measured data. [Copyright &y& Elsevier]

We used molecular dynamics (MD) simulations to investigate the diffusion of O 2 , N 2 , CH 4 , and CO 2 in a crystal of ice Ih. The results show that the diffusion mechanism for the molecules differs significantly from the interstitial mechanism that applies to small atoms such as helium. The air molecules hopped between stable sites by a new mechanism called the breaking-bond mechanism in which hydrogen bonds in the lattice are broken. The diffusion coefficients determined from the MD calculations are several orders of magnitude larger than the estimates under the assumption of the interstitial mechanism. We conclude that the repulsive interactive between the air and water molecules in ice is the dominant factor governing the diffusion mechanism. [ABSTRACT FROM AUTHOR]

• We prove the sensitivity of Raman spectroscopy to snow micro and nanostructure. • By first principles MD we model the surface vibrations of single crystal ice. • Raman spectra of fresh snow are insensitive to UV-A radiation. We investigated if the Raman spectrum of snow is affected by the highly differentiated snow morphology. The latter is subjected to continuous changes driven by the variation of ambient parameters, mainly temperature and humidity as snow progresses from freshly deposited, to compact, to icy. We measured the Raman spectrum of snow grains of different size and morphology on the temperature interval between −5.5 °C and −0.5 °C approaching the melting point. We found systematic differences with respect to bulk ice I h in the OH-stretching band of snows with different histories. We attribute the observed spectral differences to the change of the molecular arrangement of water molecules between bulk and surface sites. We investigate this characteristic via molecular dynamics DFT simulations of bulk ice and of three thin slabs cut along specific surfaces. We analysed the simulated Raman spectra and compared their distinguishing features to those of experimental spectra of snow. The Raman features of the OH-stretching band allow to distinguish among layers inside a snowpack, each layer being characterized by a different specific surface area. This is relevant to estimate the mechanical stability of the snowpack itself. The influence of UV-A irradiation on snow is discussed. [ABSTRACT FROM AUTHOR]

• Comparison of the performance of MD and DFT on the microstructure and energy of ice. • TIP4P/Ice is suited to model the microstructure and mechanical properties of ice Ih. • The fracture toughness of ice Ih was studied, and the cleavage plane was identified. • Hydrogen bond density of a surface determines the surface energy of ice Ih. This paper compares ReaxFF, SPC/E, TIP4P/2005 and TIP4P/Ice with Density Functional Theory (DFT) to identify which one should be used to model both the microstructures and mechanical properties of large size hexagonal Ice (Ih) over a long time scale (~10−9–10−6 s). According to the model performances with regards to determining the microstructure, surface energy and fracture toughness, the limitations and validities of ReaxFF and the three other potential models are discussed. It is found that hydrogen bond density determines the surface energy on the same surface. TIP4P/Ice has the smallest error and the ReaxFF force field has the largest error, up to 27.21% for the aforementioned quantities. If only modeling the microstructure of ice Ih, TIP4P/2005 and SPC/E are the most suitable water models. Moreover, the secondary prism face 11 2 ¯ 0 , with the lowest hydrogen bond density and fracture toughness, is the first cleavage plane of ice Ih. The primary prism face 1 ¯ 100 is the second cleavage plane, as shown by the surface energy and fracture toughness results of DFT and molecular dynamics (MD). [ABSTRACT FROM AUTHOR]

The Raman spectra of ice I h (H 2 O and HDO) in the temperatures range from 253 to 83 K are measured. The results show that Raman peaks shift to low- or high-wavenumber due to the influence of temperature on hydrogen bonds dynamics. Importantly, Raman shifts are linear relationship with temperatures and its slope fully reflects the change of hydrogen bonds length. Finally, Raman intensity of ice I h dependent on temperatures are also discussed. Unlabelled Image • Raman peaks shift to low- or high-wavenumber due to the influence of temperature on hydrogen bonds dynamics. • Raman shifts are linear relationship with temperatures and its slope fully reflects the change of hydrogen bonds length. • The electric field induced by temperatures causes the Raman intensity to undergo a transition at 200 K. [ABSTRACT FROM AUTHOR]