Determination of the vapor–liquid equilibrium of ionic liquid 1-Butyl-3-Methylimidazolium Hexafluorophosphate using molecular simulations

Liquid–vapor equilibrium and critical parameters of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate from molecular dynamics simulations

“…Extrapolation of experimental data (necessarily over a very large temperature interval) yielded similar values [8]. The recent work of Hernandez et al [14], who used a Dreiding FF and deduced T c from the width of the coexistence curve, however, indicated a higher value of T c = 1280 K, which is outside the range of uncertainty we attributed to our estimate. It is, therefore, of interest to find out whether this discrepancy is caused by using a different FF, a different extrapolation method to obtain the critical temperature, or other, less obvious reasons.…”

“…As mentioned in the introduction, one of the motivations for this study was to clarify the two questions raised by Hernandez et al [14] concerning our earlier work on [bmim][PF 6 ] [8]. First, they noticed the very different vapor densities obtained from our YASP and Gromacs simulations for the current force field (cf.…”

“…It is, therefore, of interest to find out whether this discrepancy is caused by using a different FF, a different extrapolation method to obtain the critical temperature, or other, less obvious reasons. In addition, Hernandez et al [14] pointed out that in our previous work, there is a large difference (exceeding an order of magnitude) between the vapor density at 800 K that is obtained using the Gromacs simulation package and the one resulting from carrying out the simulations using the YASP package for the same FF [8]. We take the opportunity to address this issue as well.…”

“…In our previous work [8], the critical temperature was obtained via Guggenheim's and Eötvös' formulas as the temperature at which the surface tension vanishes, whereas in the paper by Hernandez et al [14], Δρ was employed according to Eq. (5) with the exponent set to the Ising value of β = 0.33.…”

“…Several all-atom FFs are available for this purpose: Canongia Lopes et al developed an OPLS-type FF [12], which was later refined by Bhargava and Balasubramanian [13] to yield better results for the liquid density, the surface tension and the diffusion coefficient. Recently, Hernandez et al employed a Dreiding potential model to compute the liquid-vapor equilibrium densities [14].…”