The [EMIm] was defined to have 3 polarization groups given the importance of internal polarization in IL's as discussed by Torabifard et al. The error between the calculated and experimental data is less than 4% for each temperature. The van der Waals parameters for [EMIm] were adjusted to fit better with experimental ∆H vap (discussed below). It is possible that the parameters used for van der Waals resulted in slightly more attractive interactions at lower temperatures, but this attraction is relatively compensated at higher temperatures. [BMIm] and [diBIm] cations are starting structures and their parameters were obtained following the original method.