Studies of Hydrogen Bond Vibrations of Hydrogen-Disordered Ice Ic

Abstract

The hydrogen-disordered structure of ice, Ic, makes it difficult to analyze the vibrational normal modes in the far-infrared region (i.e., the molecular translation band). To clarify the origin of the energy-splitting of hydrogen bond vibrations in this area, a 64-molecule supercell was constructed and calculated using first-principles density functional theory. The results were in good agreement with inelastic neutron scattering experiments and our previous study of a hydrogen-ordered ice Ic model. Assisted by analytic equations, we concluded that the origin of the two hydrogen bond peaks in real ice Ic is consistent with that of hydrogen-ordered ice Ic: the peaks originate from two kinds of normal mode vibration. We categorize the four peaks in the far-infrared region recorded from inelastic neutron scattering experiments as the acoustic peak, the superposition peak, the two-hydrogen bond peak and the four-hydrogen bond peak. We conclude that the existence of two intrinsic hydrogen bond vibration modes represents a general rule among the ice family, except ice X.

Density of Phonon States in Cubic Ice Ic

“…On the contrary, as for the more elusive cubic structure of ice I, the experimental outcomes presented in the same paper cannot be assigned to a pure cubic structure, but rather to a stacking-disordered form of ice I, as the analyzed sample was obtained by warming recovered ice II and VI samples . Useful indications about the phonon dynamics can be obtained from density functional theory (DFT) simulations regarding the proton-ordered form of ice Ic, while, for its proton-disordered counterpart, they represent a quite challenging computational task that was addressed only recently …”

“…14 Useful indications about the phonon dynamics can be obtained from density functional theory (DFT) simulations regarding the proton-ordered form of ice Ic, 27 while, for its proton-disordered counterpart, they represent a quite challenging computational task that was addressed only recently. 28 In this paper, we will present the results of a combined experimental and computational study on the density of phonon state (DOPS) of H 2 O cubic ice. The same kind of investigation on the hexagonal phase Ih, obtained from the transformation of the mentioned cubic ice sample, has allowed us to quantitatively measure and successfully interpret the important differences in the phonon spectra of the two polytypes, further confirmed by centroid molecular dynamics (CMD) simulations.…”

Comparative Analysis of the Hydrogen Bond Vibrations of Ice XII

“…However, the origin of these two peaks is under continuous debate. − In our previous studies, we found two kinds of intrinsic HB vibrational modes in hydrogen-ordered ice Ic . Later, this phenomenon was also observed in ices XIV, XVI, XVII, VII, VIII, XVI, VI, and others. ,− According to the Bernal–Fowler rules, each water molecule forms an HB with four adjacent water molecules in all ice phases, and this forms a local tetrahedral structure. , We used the ideal structure of hydrogen-ordered ice Ic as the basis to analyze the lattice dynamics process.…”

“…45 Based on our previous experience, the generalized gradient approximation (GGA) exchange−correlation functional RPBE was used, as the electron density has a large gradient change. [33][34][35][36][37][38][39]46 The convergence tolerance value of energy and the self-consistent field was set to 1 × 10 −9 eV/atom. The energy cutoff was 830 eV and the k-point mesh was 2 × 2 × 2 under 0.55 GPa of pressure.…”

“…To mimic a real structure, we employed the program GenIce to create a supercell containing 24 molecules, and the hydrogens were randomly added according to the Bernal–Fowler rules. , Based on the first-principles DFT, we used the CASTEP software module for geometric optimization and phonon calculations . Based on our previous experience, the generalized gradient approximation (GGA) exchange–correlation functional RPBE was used, as the electron density has a large gradient change. − , The convergence tolerance value of energy and the self-consistent field was set to 1 × 10 –9 eV/atom. The energy cutoff was 830 eV and the k -point mesh was 2 × 2 × 2 under 0.55 GPa of pressure.…”