Thermodynamics and structure of supercooled water. II.

Abstract

Thermodynamic and structural properties of TIP4P/ice water have been studied in detail in the region of the expected occurrence of the second critical point. Various structure order parameters along with the Delaunay tessellation and density histogram have been used with a focus on their ability and mutual consistency to provide the necessary information. Whereas density histograms clearly show the bimodal distribution corresponding to the coexistence of two metastable density states, most of the standard structural parameters provided only information about the increase in the level of molecular order with lowered temperature. Only the parameter called the local structure index and parameters based on the Delaunay tessellation provided information consistent with the density histogram. The bimodality in these parameters has been connected to the anomalous behavior of the isothermal compressibility which increases in the supercooled region gaining the λ-shape form which a sign of the presence of the critical point. In addition, an attempt to link the structures of supercooled water to that of an underlying disordered ice is made.