Molecular dynamics (MD) simulations were applied to investigate the liquid-liquid equilibria of water and dipropylene glycol dimethyl ether (DMM) based on all-atom OPLS force fields and simple point charge (SPC) water model. The default combining rules (geometric means) for describing interactions between water and ether molecules were modified by fitting hydration free energies of dimethyl ether and diethyl ether. The difference of Gibbs free energies (Delta G) was calculated using the thermodynamic integration (TI) method. Extensive simulations were carried out in order to reach high precision in the predicted free energies. The average uncertainties in calculated Delta G are 0.8 kJ/mol for DMM and 0.3 kJ/mol for water. From the calculated Delta G(mix), the mutual solubility of the binary mixture was predicted using the double tangent method at four temperatures ranging from 283 K to 353 K and 1 atm. (c) 2011 Elsevier B.V. All rights reserved.