Structure of soft-sphere dipolar fluids

We examine the structure of soft-sphere dipolar (SSD) fluids as a function of density and applied field. Besides being fundamental test systems for theory, dipolar fluids are models for ferrofluids. We show that chain formation is a fundamental characteristic of the SSD fluid resulting in a phase diagram much different from fluids with an isotropic potential. In particular, two-phase liquid-gas coexistence does not appear to occur in the absence of an applied field. In an applied field, phase coexistence does occur and we discuss the structure of the SSD system in the vicinity of the critical point. In contrast to expectations, the SSD does not model ferrofluids well. An additional attractive interaction beyond the dipolar interaction is needed to model ferrofluids. © 1995 The American Physical Society.