Manifestations of the structural origin of water's anomalies in the heterogeneous relaxation on the potential energy landscape

Liquid water is well-known for its intriguing thermodynamic anomalies in both the normal and the supercooled states. The phenomenological two-state models based on the assumption of the existence of two types of competing local states in liquid water have been extremely successful in describing the thermodynamic anomalies of water. However, the precise structural and energetic features of these two types of competing local states in liquid water still remain elusive. In this study, we have employed a predefined structural order parameter-free approach to unambiguously identify the two types of interconvertible local states with significantly different structural and energetic features in the TIP4P/2005 liquid water. This identification is based on the heterogeneous relaxation of the thermally equilibrated structures in the potential energy landscape (PEL) during the steepest-descent energy minimization. We have further established a direct relationship between the population fluctuation of the two types of local states and the anomalous thermodynamic behavior of supercooled water. Additionally, this study unravels the signatures of the supercooled water's anomalies encoded in the topography of the PEL of the system. We believe that the generality of the approach proposed here would enable it to be applicable to a broad range of liquids, not necessarily molecular, to provide the precise molecular origin of bulk liquid properties.