Structure and OH-stretch spectroscopy of low- and high-density amorphous ices

We use the E3B water simulation model (which explicitly includes three-body interactions) and molecular dynamics simulations to study the structure of low-and high-density amorphous ices. We find that the interstitial molecule in high-density amorphous ice, which is responsible for the higher density, is not hydrogen bonded to the central molecule or its nearest neighbors. This molecule enforces a wider range of local environments as demonstrated by the tetrahedral order parameter, whereas the local structure of low-density amorphous ice is more ordered. We also present theoretical vibrational spectra (infrared, Raman, and two-dimensional infrared) for the amorphous phases, for both HOD/D2O and H2O. The results are in qualitative agreement with experiment and reflect the fact that low-density amorphous ice is more ordered, with stronger hydrogen bonds, compared to high-density amorphous ice. For both the structural analysis and spectral calculations, we compare the results for the amorphous ices with those for crystalline ice Ih and supercooled water. (C) 2014 AIP Publishing LLC.