Extensive Accuracy Test Of The Force-Field-Based Quasichemical Method Pac-Mac

We present a comprehensive evaluation of the recently developed pair configuration to molecular activity coefficient (PAC-MAC) method. PAC-MAC is a force-field based quasichemical method for rapid calculation of binary phase diagrams. The accuracy of the method is tested by comparing the calculated excess mixing free energy with experimental data for 1092 binary mixtures. The root mean squared error (RMSE) is shown to be 0.15 k(B)T. Furthermore, a comparison with UNIFAC and molecular simulations is performed. UNIFAC shows a significantly higher accuracy (RMSE: 0.07 k(B)T), whereas molecular simulations lead to comparable results. The accuracy of both molecular simulations as well as PAC-MAC depends highly on the used force field. The binary parameters of UNIFAC are optimized using experimental miscibility data, whereas the force field parameters are not. Therefore, a better performance of UNIFAC is expected. A concise data set shows the capacity of PAC-MAC in predicting results obtained using Monte Carlo simulations.