Water-like anomalies for core-softened models of fluids

We use one-dimensional (1d) [1] and two-dimensional (2d) [2] core-softened potentials to develop a physical picture for some of the anomalies present in liquid water. The core-softened potential mimics the effect of hydrogen bonding. We study the 1d system analytically and the 2d system using molecular dynamic simulations. In the 2d system, we observe in the liquid phase three types of anomalies: (i) an increase in specific volume upon cooling, (ii) an increase in isothermal compressibility upon cooling, and (iii) an increase in the diffusion coefficient with pressure. We relate the anomalies to the existence of two different local structures in the liquid phase, which resemble high- and low-density crystalline phases. We also discuss the possible existence of a second critical point located in the low-temperature region of the metastable liquid below the crystallization line. [1] M. R. Sadr-Lahijany et al., PRE 60 (1999) 6714. [2] M. R. Sadr-Lahijany et al., PRL 81 (1998) 4895.