| This work focuses on the efficient implementation of Monte Carlo methodologies in the study of vapor-liquid transitions. Fluids with both short and long range forces have been studied. Accurate estimates of critical points and critical point exponents have also been extracted.; The first part of this work is devoted to the simplest possible ionic fluid, the restricted primitive model. Conventional simulation methods are not efficient due to the strong magnitude of the Coulomb force which causes the system to associate. Biased moves, capable of moving the system fast through phase space, have been developed. The phase envelope is obtained by implementation of the previous moves in the Gibbs ensemble method.; The quality of the coexistence data from the Gibbs ensemble simulations is not considered satisfactory, however, and the remaining part of this work thus focuses on methods that appear to be more efficient. A new technique, density scaling Monte Carlo, is applied to the primitive model in two and three dimensions. The fluid phase of the two-dimensional system consists of three different phases: insulating vapor, conducting vapor and liquid. The well known low-density Kosterlitz-Thouless (KT) phase transition, is found to become vapor-liquid coexistence at finite densities. The KT line terminates close to the vapor-liquid critical point.; In addition, two recent approaches originally proposed for Ising-like systems have been applied to the models of interest. In the histogram reweighting method, data obtained at a fixed set of parameters are extrapolated to a different set of values. The multicanonical preweighting scheme artificially enhances the sampling of configurations with intrinsically low probability. The vapor-liquid transition of the square-well fluid is examined in detail, in the framework of the grand canonical ensemble.; Finally, the approach to criticality has been studied in detail, both for the square-well fluid and for the primitive model, by utilizing finite-size scaling techniques. The increase in the range of the square-well interaction forces a reduction in the extent of the critical (Ising) region. The primitive model appears to obey the Ising universality class as well. However, the results are not sufficiently accurate to allow for definite conclusions. |
