  The study of liquid-liquid phase transition has attracted considerable
attention. One interesting example of such phenomenon is phosphorus for which
the existence a first-order phase transition between a low density insulating
molecular phase and a conducting polymeric phase has been experimentally
established. In this paper, we model this transition by an ab-initio quality
molecular dynamics simulation and explore a large portion of the liquid section
of the phase diagram. We draw the liquid-liquid coexistence curve and determine
that it terminates into a second-order critical point. Close to the critical
point, large coupled structure and electronic structure fluctuations are
observed.
