Modelling of the structure and vibrational properties of LDA, HDA, and VHDA amorphous ices

The models of three known amorphous ice structures—low-density (LDA), high-density (HDA) and very-high-density (VHDA) amorphous ices have been obtained using sequential steps of molecular dynamics simulation and the additional optimization scheme within the lattice dynamics approach at the different cell parameters. It has been shown that this combined approach leads to a more accurate and detailed structural description of HDA and LDA ices and yields results that are in excellent agreement with experiment. The dynamic properties of obtained structures have been analyzed within the lattice dynamics approach. It has been shown that in all considered structures there exist some extended vibrational modes, which involve up to 70% of molecules. These modes apparently are a consequence of existence of hydrogen bonds network in amorphous ices.