Island of Vapor-Liquid Coexistence in Dipolar Hard-Core Systems

Contrary to theoretical expectations, spheres with central point dipoles have recently been shown not to exhibit a vapor-liquid phase transition; instead the system forms chains of dipoles in a nose-to-tail configuration. We study hard spherocylinders with central longitudinal point dipoles, and induce an island of vapor-liquid coexistence by elongating the molecules. As the length of the molecule is increased, a vapor-liquid envelope appears. After further elongation this region diminishes and then disappears; the system now exhibits antiparallel side-by-side chains of dipoles.