Are all-atom any better than united-atom force fields for the description of liquid properties of alkanes? 2. A systematic study considering different chain lengths

Abstract

Our previous study assessed the performance of 12 different force fields in describing the liquid phase of n-octane. The present study extends the analysis to n-alkanes of longer chain lengths. The 6 best force fields considered in our previous study were evaluated regarding their accuracy at reproducing the density, heat of vaporization, surface tension, and viscosity of n-dodecane, n-hexadecane, n-eicosane, n-tetracosane, and n-octacosane. The considered force fields were ranked based on the root-mean-squared deviation and normalized root-mean-squared deviation over different properties and compounds. This deviation analysis, combined with the fitting of linear relationships, presented a clear picture of the quality of the chosen models in reproducing the properties of interest. The all-atom version of the CHARMM (CHARMM-AA) and NERD models present a premature solidification behavior. In agreement to the previous study that was limited to n-octane, the united-atoms models led to comparable or even better results than all-atom models in reproducing the properties of liquid phases of alkanes. Overall, the united-atom GROMOS force field performed systematically better than the other force fields in reproducing the liquid-phase properties of the considered alkane molecules.