Anomalous phase behavior in a model fluid with only one type of local structure.

We present evidence that the concurrent existence of two populations of particles with different effective diameters is not a prerequisite for the occurrence of anomalous phase behaviors in systems of particles interacting through spherically symmetric unbounded potentials. Our results show that an extremely weak softening of the interparticle repulsion, which yields a single nearest-neighbor separation, is able to originate a wide spectrum of unconventional features including reentrant melting, solid polymorphism, as well as thermodynamic, dynamic, and structural anomalies. These findings extend the possibility of anomalous phase behavior to a class of systems much broader than currently assumed.