Liquid-Liquid Phase Transition: Evidence from Simulations

We report, using extensive molecular dynamics simulations of a one-component model system, a first-order liquid-liquid phase transition. Specifically, by evaluating the pressure-density isotherms above and below a critical temperature, we find the presence of two coexisting phases differing by $\ensuremath{\sim}15%$ in density. Moreover, system points in an unstable region decompose into two different spatially separated phases. We identify the two phases, characterized by different local structures and local dynamics, by studying the static structure factor $S(q)$ at small wave vector $q$.