  Monte Carlo simulations are presented for a coarse-grained model of real
quadrupolar fluids. Molecules are represented by particles interacting with
Lennard-Jones forces plus the thermally averaged quadrupole-quadrupole
interaction. The properties discussed include the vapor-liquid coexistence
curve, the vapor pressure along coexistence, and the surface tension. The full
isotherms are also accessible over a wide range of temperatures and densities.
It is shown that the critical parameters (critical temperature, density, and
pressure) depend almost linearly on a quadrupolar parameter $q=Q^{*4} /T^*$,
$Q^*$ is the reduced quadrupole moment of the molecule and $T^*$ the reduced
temperature.
  The model can be applied to a variety of small quadrupolar molecules. We
focus on carbon dioxide as a test case, but consider nitrogen and benzene, too.
Experimental critical temperature, density and quadrupolar moment are
sufficient to fix the parameters of the model. The resulting agreement with
experiments is excellent and marks a significant improvement over approaches
which neglect quadrupolar effects. The same coarse-grained model was also
applied in the framework of Perturbation Theory (PT) in the Mean Spherical
Approximation (MSA). As expected, the latter deviates from the Monte Carlo
results in the critical region, but is reasonably accurate at lower
temperatures.
