Coexistence in dipolar fluids in a field

We examine two phase coexistence for soft sphere dipolar fluids in an applied field, H. Besides being a fundamental test system for theory, dipolar fluids are used as models for ferrofluids. Gibbs ensemble simulations were performed to determine the coexistence curve and an estimate of the critical temperature, Tc, and density, ρc, as a function of applied magnetic field. In zero field we show that coexistence most likely does not occur and if it does can only do so in a narrow range of densities much lower than predicted theoretically. We discuss the structure of soft sphere dipolar systems, which turns out to be much more complex than previously thought. © 1994 The American Physical Society.