Long-ranged orientational order in dipolar fluids

Based on density-functional theory we study the occurrence of a ferroelectric phase in Stockmayer fluids. Because of the long-ranged dipolar forces the corresponding bulk phase diagrams depend on both the shape of the sample and the character of the dielectric surrounding. For ellipsoidal samples with different aspect ratios at high temperatures we find a line of critical points, whereas at temperatures below a tricritical point the phase transition is first order. The behavior near the continuous phase transitions is analyzed by a systematic Landau expansion.