Modeling the polymorphic transformations in amorphous solid ice

The description of various amorphous phases of ices has been performed on a molecular level in order to study the nature of amorphous polymorphism in a water system. The models of very high-, high- and low-density amorphous (VHDA, HDA and LDA, respectively) ices have been constructed. The molecules are located in their equilibrium states and the structure of the networks is characterized by the absence of long-range atomic order, but short-range order is still present. The thermodynamic properties of VHDA, HDA and LDA ices have been determined using the molecular dynamics and lattice dynamics methods. It has been found that at low temperatures the transformation LDA → HDA is a real phase transition in the classical sense. In the case of HDA → VHDA, the same transition has been found only in negative pressure regions. At positive pressure the transformation from the metastable phase HDA to the thermodynamically stable phase VHDA can be classified as a continuous one.