Effective potentials for liquid simulation of the alternative refrigerants HFC-134a (CF3CH2F) and HFC-125 (CF3CHF2)

Isotropic atom-atom potentials for use in liquid simulations of 1,1,1,2-tetrafluoroethane (HFC-134a; CF3CH2F) and pentafluoroethane (HFC-125; CF3CHF2) are constructed using effective interactions. These semirigid molecules have interaction centres at the atomic sites and internal rotation about the CC bond. Intermolecular interactions consist of repulsion-dispersion and Coulombic parts. The internal rotation about the CC bond is described by a small angle cosine Fourier expansion in the dihedral angle. The potential functions are adjusted to give simulated liquid properties for temperatures between 0.5 (TTC) and 0.9 (TTC) on the saturated liquid curves. oposed potentials are used in constant pressure-constant temperature and constant volume-constant temperature molecular dynamics simulations of saturated liquid HFC-134a and HFC-125. Simulated results for thermodynamic, structural and dynamic properties are presented, and compared with experimental data where available.