Path-integral simulation of ice I_{h}: The effect of pressure (original) (raw)
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Ab initio simulation of hydrogen bonding in ices under ultra-high pressure
The Journal of Chemical Physics, 2012
In this article, as continuation of the previous publication (P. Zhang, L. Tian, Z. P. Zhang, G. Shao, and J. C. Li, J. Chem. Phys. 137, 044504 (2012)), we report a series of computational simulation results for ices using ab initio DFT methods. The results not only reproduced the main feature of inelastic neutron scattering spectra for ice Ih, but also other phases of ice such as VII and VIII. Furthermore, pressure dependent simulations for ice I and VIII have led us to obtain the spectra for the symmetrical structure of ice X. The transition from normal ice to the symmetrical form shows an extraordinary behaviour of H-bonding in term of vibrations associated with inter-and intra-molecular bonds, revealing a range of phenomena which was not seen before.
Isotope effects in ice Ih: A path-integral simulation
The Journal of Chemical Physics, 2011
Ice Ih has been studied by path-integral molecular dynamics simulations, using the effective q-TIP4P/F potential model for flexible water. This has allowed us to analyze finite-temperature quantum effects in this solid phase from 25 to 300 K at ambient pressure. Among these effects we find a negative thermal expansion of ice at low temperatures, which does not appear in classical molecular dynamics simulations. The compressibility derived from volume fluctuations gives results in line with experimental data. We have analyzed isotope effects in ice Ih by considering normal, heavy, and tritiated water. In particular, we studied the effect of changing the isotopic mass of hydrogen on the kinetic energy and atomic delocalization in the crystal as well as on structural properties such as interatomic distances and molar volume. For D2O ice Ih at 100 K we obtained a decrease in molar volume and intramolecular O-H distance of 0.6% and 0.4%, respectively, as compared to H2O ice.
High-density amorphous ice: A path-integral simulation
The Journal of Chemical Physics, 2012
Structural and thermodynamic properties of high-density amorphous (HDA) ice have been studied by path-integral molecular dynamics simulations in the isothermal-isobaric ensemble. Interatomic interactions were modeled by using the effective q-TIP4P/F potential for flexible water. Quantum nuclear motion is found to affect several observable properties of the amorphous solid. At low temperature (T = 50 K) the molar volume of HDA ice is found to increase by 6%, and the intramolecular O-H distance rises by 1.4% due to quantum motion. Peaks in the radial distribution function of HDA ice are broadened respect to their classical expectancy. The bulk modulus, B, is found to rise linearly with the pressure, with a slope ∂B/∂P = 7.1. Our results are compared with those derived earlier from classical and path-integral simulations of HDA ice. We discuss similarities and discrepancies with those earlier simulations.
Elastic constants of ice Ihas described by semi-empirical water models
The Journal of Chemical Physics, 2019
Using molecular dynamics simulations we compute the elastic constants of ice I h for a set of 8 frequently used semiempirical potentials for water, namely the rigid-molecule SPC/E, TIP4P, TIP4P2005, TIP4P/Ice and TIP5P models, the flexible-molecule qTIP4P/Fw and SPC/Fw models and the coarse-grained atomic mW potential. In quantitative terms, the mW description gives values for the individual stiffness constants that are closest to experiment, whereas the explicit-proton models display substantial discrepancies. On the other hand, in contrast to all explicit-proton potentials, the mW model is unable to reproduce central qualitative trends such as the anisotropy in Young's modulus and the shear modulus. This suggests that the elastic behavior of ice I h is closely related to its molecular nature, which has been coarse-grained out in the mW model. These observations are consistent with other recent manifestations concerning the limitations of the mW model in the description of mechanical properties of ice I h .
Hydrogen Bonds and van der Waals Forces in Ice at Ambient and High Pressures
Physical Review Letters, 2011
The first principles methods, density-functional theory and quantum Monte Carlo, have been used to examine the balance between van der Waals (vdW) forces and hydrogen bonding in ambient and high-pressure phases of ice. At higher pressure, the contribution to the lattice energy from vdW increases and that from hydrogen bonding decreases, leading vdW to have a substantial effect on the transition pressures between the crystalline ice phases. An important consequence, likely to be of relevance to molecular crystals in general, is that transition pressures obtained from density-functional theory exchange-correlation functionals which neglect vdW forces are greatly overestimated.
Structural studies of low temperature ice Ih using a central force potential model
The Journal of Chemical Physics, 1983
The revised central force potentials of Stillinger and Rahman [J. Chern. Phys. 68. 666 11978)] are used to study the binding energy, structure, and multipole moments of a periodic ice Ih sample with a unit cell of 192 water molecules. The initial configuration for the unit cell has each oxygen in a wurtzite structure and intramolecular H-O-H angles symmetrically positioned in the tetrahedral 0-0-0 angles. Hydrogens are placed such that the total dipole moment for the unit cell is zero and the diagonal quadrupole moments are small I :S 10-28 esu cm 2). Subject to these restrictions, a static energy minimization on the periodic ice crystal yields an optimal 0-0 separation, intramolecular O-H distance, and intramolecular H-O-H angle of 2.78, 0.972 A, and 101.0", respectively. Starting from this idealized wurtzite configuration, Metropolis Monte Carlo runs on the periodic system are made at 20 and 200 K. At 20 K. the equilibrated system has an average intermolecular potential energy per molecule of-15.2 kca1!mol and structure factors which have decreased to about 80% of the initial values. The dipole moment for the unit cell is ~ 3 D. The equilibrated system at 200 K appears to be modified only by temperature dependent vibrational effects.
Ab initio simulation of the ice II structure
The Journal of Chemical Physics, 2003
We have carried out ab initio simulations on the high-pressure polymorph of solid water, ice II, a phase for which there is a surprising lack of experimental data. We report our calculated third-order Birch-Murnaghan equation of state for ice II: the zero pressure and temperature density, 0 ϭ1240.27Ϯ0.62 kg m Ϫ3 , bulk modulus, K 0 ϭ16.18Ϯ0.12 GPa, with the first pressure derivative of the bulk modulus, K 0 Ј , fixed equal to 6.0. These parameters, the unit cell dimensions, and the atomic positions are in good agreement with experimental values. We also describe the way in which the change in unit cell volume is accommodated within the structure, primarily by contraction of the distance between neighboring hexagonal tubes-the principal structural element of ice II. This is in agreement with existing experimental data.
In this document we provide brief descriptions of the ice structures and details of the simulations with DFT, vdW corrected DFT, and DMC. Details of additional calculations done to ensure the accuracy of the results in the main manuscript are reported. We also report results illustrating the sensitivity of the lattice energies of certain ice phases to the percentage of Hartree-Fock exchange used in the hybrid DFT calculations. * angelos.michaelides@ucl.ac.uk
Pressure-Induced Phase Transitions of Proton-Ordered Ices at the Low Temperature Limit
Journal of Computer Chemistry Japan
The Gibbs free energies of proton-ordered ices were estimated by molecular dynamics simulations. The ordered structures were obtained using NTV ensemble molecular dynamics of cells with small numbers of molecules, where the cut off distance for short range interaction was 1.4 10 -9 m. The internal energy and volume were obtained by NTp molecular dynamics simulations at T = 1 K for each type of ice, where the cut off distance for short range interaction was half of the unit cell and the Ewald method was used to determine coulombic interaction. The infinite number limits in the internal energies of each ice type at T = 1 K were estimated. The enthalpy temperature dependence was calculated and the low temperature limit was estimated to obtain the Gibbs free energy at low temperatures. Phase transition pressures obtained were satisfactory when compared with the experimental results, at least qualitatively.
Journal of Chemical Theory and …, 2005
The absolute free energies of several ice polymorphs were calculated using thermodynamic integration. These polymorphs are predicted by computer simulations using a variety of common water models to be stable at low pressures. A recently discovered ice polymorph that has as yet only been observed in computer simulations (Ice-i) was determined to be the stable crystalline state for all the water models investigated. Phase diagrams were generated, and phase coexistence lines were determined for all of the known low-pressure ice structures. Additionally, potential truncation was shown to play a role in the resulting shape of the free energy landscape.