Phase diagram of the double-Gaussian potential

Isotropic pair potentials that are bounded at the origin have from time to time been proposed as models of the effective interaction between aggregates of interest in soft-matter physics. We present a thorough study of the phase behavior of point particles interacting through a potential which combines a bounded short-range repulsion with a much weaker attraction at moderate distances, both of Gaussian shape. Two different strengths of attraction were considered, a smaller and a larger one. In the former case, the phase diagram of the double-Gaussian model (DGM) is quite rich, showing two fluid phases and four distinct solid phases. Using free-energy calculations, the various regions of confluence of three distinct DGM phases have all been characterized in detail. Moreover, two lines of reentrant melting are found, and for each of them a rationale is provided in terms of the elastic properties of the solid phases. In the other case of strong attraction, yet not too strong to make the system thermodynamically unstable, the phase behavior of the DGM system is closely reminiscent of water.