Lennard-Jones force field parameters for cyclic alkanes from cyclopropane to cyclohexane

Abstract

Lennard-Jones (LJ) force field parameters for cyclic alkanes from cyclopropane to cyclohexane are proposed. The molecular geometry is obtained from quantum mechanical calculations. The united-atom approach is applied by initially locating each site at the carbon atom position and subsequently changing the site–site distance; thereby, the LJ parameters and the site–site distance are optimized to vapor–liquid equilibrium (VLE) data, i.e., vapor pressure, saturated liquid density and enthalpy of vaporization. These new cycloalkane force fields are able to describe the VLE data with deviations of a few percent. Furthermore, self-diffusion coefficient, shear viscosity and thermal conductivity are calculated by molecular dynamics simulation and the Green–Kubo formalism. For the smaller two cycloalkanes, i.e., cyclopropane and cyclobutane, the predicted transport properties are in good agreement with the available experimental data. However, the force fields for cyclopentane and cyclohexane specified in this way do not predict transport properties with the desired accuracy. Therefore, they are re-optimized to experimental data on VLE properties and self-diffusion coefficient simultaneously. Then, also the other transport properties meet the experimental data well.