Dynamical properties of supercooled water close to the liquid–liquid coexistence lines, andtheir relation to those at ambient conditions

Abstract

We report results of molecular dynamics simulations of supercooled bulk water at 180 K,close to the liquid/liquid coexistence lines recently discovered in the supercooled regime,both experimentally and by computer simulations. Despite the considerable differences inthe densities of the three states considered, the obtained velocity autocorrelation functionsdisplay very similar behaviour in every case. On the other hand, the corresponding spectrashow the presence of three well-defined modes. The two modes at higher frequencies areassigned to the symmetric and asymmetric stretching motions, respectively, whereas thelowest frequency mode to the bending and torsional motions in clusters of fivehydrogen-bonded water molecules. A careful fitting procedure demonstrates thepresence of such clusters also in the normal liquid phase of water at ambientconditions.