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

• New rigid united-atom LJ force fields are proposed.
• Molecular geometry based on QM calculations.
• Optimization to VLE data and VLE + self-diffusion.
• VLE data is reproduced within a few percent.
• Deviation of calculated transport properties below 20%.

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.

New LJ force field parameters for small cycloalkanes are proposed. These rigid models are optimized to VLE data. Transport properties are also assessed. In the figure, the saturated density of the developed force fields (empty symbols) is compared with correlations of experimental data or equations of state (solid lines).Figure optionsDownload as PowerPoint slide