Can existing models qualitatively describe the mixing behavior of acetone with water?

The Helmholtz free energy of neat water, neat acetone, and acetone-water mixtures of various compositions covering the acetone mole fraction range of 0.02-0.26 is calculated at 300 K by computer simulation using the method of thermodynamic integration. In the calculations the mixtures of Kirkwood-Buff force field (KBFF) acetone with both TIP4P and SPC/E water are considered. The Helmholtz free energy of mixing calculated from the free energy difference of the mixture and of the two neat phases is found to be positive at each composition considered, indicating that the studied systems are thermodynamically unstable. The range of immiscibility is estimated to extend from the acetone mole fraction value below 0.01 to about 0.28 for both model pairs. Since a previous investigation [A. Perera and F. Sokolic, J. Chem. Phys. 121, 11272 (2004)] showed that, with the exception of SPC/E water and KBFF acetone, acetone-water model pairs exhibit demixing behavior, the present result points out that currently no existing acetone model can qualitatively reproduce the phase behavior of acetone-water mixtures, i.e., the well known experimental fact that acetone is miscible with water in any proportion.