Particle size and phase equilibria in classical logarithmic fluid

An interparticle interaction potential has been recently proposed in studies of condensate-like systems described by logarithmically nonlinear equations, such as the superfluid helium-4 and Korteweg-type melts. It has the shape of a Gaussian multiplied by a linear function and can switch between the attraction and repulsion regimes as the distance varies. We consider a classical fluid model with a discretized version of this potential in Monte Carlo molecular simulations in the Gibbs ensemble. We demonstrate a two-phase system consisting of a dense "liquid" phase in coexistence with a significantly less dense "vapour" phase. For computations, the particle size term in the potential was varied to determine its effect on both the phase envelope and the critical point of the system. It is found that the logarithm of the dimensionless critical temperature decreases in a sigmoid fashion with increasing particle size, while the critical density may be directly proportional to the particle size. (paper)