Within the last 15 years, some equation of state (EOS) models have been developed that are based on well-defined physical models, in contrast to empirical, e.g. cubic, EOS models. In these models, the parameters have a clear physical meaning. On this basis we show how quantum mechanics can be used to compute molecular parameters for a modified PC-SAFT EOS. Specifically, we report a method to estimate pure compound EOS paramters from quantum mechanically determined molecular paramters and a method where one experimental data point is sufficient, together with the molecular parameters, to determine the required EOS paramters. Finally, we compare the results of predicted mixture properties with experimental data.