Generic mechanism for generating a liquid–liquid phase transition

Recent experimental results1 indicate that phosphorus—a single-component system—can have a high-density liquid (HDL) and a low-density liquid (LDL) phase. A first-order transition between two liquids of different densities2 is consistent with experimental data for a variety of materials3,4, including single-component systems such as water5,6,7,8, silica9 and carbon10. Molecular dynamics simulations of very specific models for supercooled water2,11, liquid carbon12 and supercooled silica13 predict a LDL–HDL critical point, but a coherent and general interpretation of the LDL–HDL transition is lacking. Here we show that the presence of a LDL and a HDL can be directly related to an interaction potential with an attractive part and two characteristic short-range repulsive distances. This kind of interaction is common to other single-component materials in the liquid state (in particular, liquid metals2,14,15,16,17,18,19,20,21), and such potentials are often used to describe systems that exhibit a density anomaly2. However, our results show that the LDL and HDL phases can occur in systems with no density anomaly. Our results therefore present an experimental challenge to uncover a liquid–liquid transition in systems like liquid metals, regardless of the presence of a density anomaly.