A molecular dynamics study of liquid aliphatic alcohols: simulation of density and self-diffusion coefficient using a modified OPLS force field

Abstract

A set of 13 aliphatic alcohols was modelled by molecular dynamics simulations at temperatures from 288 to 338 K using the optimised potential for liquid simulations (OPLS) united-atom force field, the OPLS all-atom force field and the OPLS all-atom force field with modified partial charges of the hydroxyl group. The set includes primary and secondary alcohols, and mono-, di- and trialcohols, and covers a broad range of polarities from log P = − 0.74 (methanol) to log P = 2.9 (octanol). The density, the radial distribution function, the self-diffusion coefficient and the dielectric constant were evaluated. A long equilibration time of at least 50 ns and a large size of the molecular system of more than 75,000 atoms were used. Except for glycerol, the OPLS all-atom force field reliably reproduced the experimentally determined density with deviations of less than 4% over the whole temperature range. In contrast, the modelled self-diffusion coefficient deviated from its experimental value by up to 55%. To modify the force field, the partial charges of the hydroxyl group were varied by up to 3%. Using the modified OPLS force field, the deviation of the self-diffusion coefficients from their experimental values decreased to less than 19%, while the densities changed by less than 1%.

Keywords::

• molecular dynamics simulation
• alcohols
• density
• self-diffusion coefficient
• dielectric constant

Acknowledgements

We are grateful for insightful discussions with Jens Abildskov (DTU Lyngby) and Joachim Gross (University of Stuttgart). T.K. thanks Sascha Rehm for the help with creating the models of the organic liquids and Sven Benson for helpful suggestions for the computation of the self-diffusion coefficient. The authors acknowledge the German Science Foundation DFG (Sonderforschungsbereich 716) for financial support and the High Performance Computing Center Stuttgart for kindly providing computational resources.