Improved GAFF2 parameters for fluorinated alkanes and mixed hydro- and fluorocarbons.

We present improved molecular mechanics models for perfluorocarbons and mixed hydro- and fluorocarbons, based on the GAFF2 force field. Benchmarking was performed for a series of single molecule geometries and for condensed phases, namely self-assembled monolayers comprising perfluoro-octadecane phosphonic acids. From this, considerable improvement of the torsion angles is demonstrated. Apart from structural characterization, we also illustrate the implications of the old and new GAFF2-type models for mechanical properties by mimicking self-assembled monolayer indentation.