Reentrant and Isostructural Transitions in a Cluster-Crystal Former

We study the low-temperature behavior of a simple cluster-crystal forming system through simulation. The phase behavior is found to be hybrid between the Gaussian core and penetrable sphere models. The system additionally exhibits a series of reentrant crystallization and melting loops as well as critical isostructural transitions between crystals of different occupancy. Due to the creation and annihilation of lattice sites, the system further shows an unusual and intriguing softening upon compression.