EXCESS PROPERTIES OF DIPOLAR AND NONPOLAR FLUID MIXTURES FROM NPT MOLECULAR-DYNAMICS SIMULATIONS

Thermodynamic properties of mixtures of dipolar and non-polar linear m olecules are obtained from NpT molecular dynamics (MD) simulations and are compared with previously reported results from NVT MD simulations , and from a perturbation theory for polar non-spherical molecular flu ids. The interactions between the particles of the mixtures are all of the same two-centre Lennard-Jones (2CLJ) type, of elongation L = 0 . 505 with an additional axial point dipole on the polar molecules. For these mixtures NpT MD simulations were performed for various dipole mo ments and compositions for a statepoint previously investigated by NVT MD simulations. We show that the approximation used to calculate exce ss Gibbs energies at constant pressure from the NVT ensemble gives cor rect results even if it is more computationally demanding. Additionall y, we present results for the excess enthalpy and the excess volume, w hich are in good agreement with perturbation theory.