Homogeneous Nucleation of [dmim+][Cl-] from its Supercooled Liquid Phase: A Molecular Simulation Study

We have used molecular simulations to study the homogeneous nucleation of the ionic liquid [dmim+][Cl−] from its bulk supercooled liquid at 340 K. Our combination of methods include the string method in collective variables (Maragliano et al., J. Chem. Phys. 125:024106, 2006), Markovian milestoning with Voronoi tessellations (Maragliano et al J Chem Theory Comput 5:2589, 2009), and order parameters for molecular crystals (Santiso and Trout J Chem Phys 134:064109, 2011). The minimum free energy path, the approximate size of the critical nucleus, the free energy barrier and the rates involved in the homogeneous nucleation process were determined from our simulations. Our results suggest that the subcooled liquid (58 K of supercooling) has to overcome a free energy barrier of ~85 kcal/mol, and has to form a critical nucleus of size ~3.4 nm; this nucleus then grows to form the monoclinic crystal phase. A nucleation rate of 6.6 × 1010 cm−3 s−1 was determined from our calculations, which agrees with values observed in experiments and simulations of homogeneous nucleation of subcooled water.