Structural anomalies for a three dimensional isotropic core-softened potential

Abstract

Using molecular dynamics simulations we investigate the structure of a system of particles interacting through a continuous core-softened interparticle potential. We found for the translational order parameter, t, a local maximum at a density $ρ_{t-max}$ and a local minimum at $ρ_{t-min} > ρ_{t-max}$. Between $ρ_{t-max}$ and $ρ_{t-min}$, the $t$ parameter anomalously decreases upon pressure. For the orientational order parameter, $Q_6$, was observed a maximum at a density $ρ_{t-max}< ρ_{Qmax} < ρ_{t-min}$. For densities between $ρ_{Qmax}$ and $ρ_{t-min}$, both the translational (t) and orientational ($Q_6$) order parameters have anomalous behavior. We know that this system also exhibits density and diffusion anomaly. We found that the region in the pressure-temperature phase-diagram of the structural anomaly englobes the region of the diffusion anomaly that is larger than the region limited by the temperature of maximum density. This cascade of anomalies (structural, dynamic and thermodynamic) for our model has the same hierarchy of that one observed for the SPC/E water.