Molecular simulations according to the NpT + test particle method are used for the determination of vapour-liquid phase equilibria of six model potentials of the two-centre Lennard-Jones plus point quadrupole (2CLJQ) type. By fitting to experimental saturation properties of carbon dioxide, an optimized effective 2CLJQ potential for this substance is found to have the parameters is-an-element-of/k 125.317 K, sigma = 3.0354 angstrom, L = l/sigma = 0.699, and Q*2 = Q/is-an-element-of sigma5 = 3.0255; the resulting quadrupole moment Q differs from the most recent experimental value by only 9%. Using this potential, densities and enthalpies of carbon dioxide are obtained again by molecular simulations as functions of temperature and pressure in large parts of the fluid region extending from 230 to 570 K, and pressures up to 400 MPa. The results show that effective potentials obtained by fitting to experimental saturation properties also yield good predictions of the thermodynamic properties for polar substances.