Vapor-liquid coexistence in fluids of charged hard dumbbells

Vapor-liquid coexistence in fluids of charged hard dumbbells, each made up of two oppositely charged hard spheres with diameters sigma and separation d, has been studied using grand-canonical Monte Carlo simulations. In the limit d/sigma -> 0, and with the temperature scaled accordingly, the system corresponds to dipolar hard spheres. For separations in the range 0.3 < d/sigma <= 1 the coexisting vapor phase contains compact clusters. For separations in the range 0.1 <= d/sigma < 0.3 the coexistence is between a chainlike vapor and a networklike liquid. Finite-size effects preclude the simulation of the coexistence in systems with d/sigma < 0.1, but extrapolations of the results to d/sigma -> 0 yield estimates of the apparent critical parameters for dipolar hard spheres. (C) 2007 American Institute of Physics.