A transferable coarse-grained model for hydrogen-bonding liquids

We present here a recent development of a generalized coarse- grained model for use in molecular simulations. In this model, interactions between coarse- grained particles consist of both van der Waals and explicit electrostatic components. As a result, the coarse- grained model offers the transferability that is lacked by most current effective- potential based approaches. The previous center- of- mass framework ( P. A. Golubkov and P. Ren, J. Chem. Phys., 2006, 125, 64103) is generalized here to include arbitrary off- center interaction sites for both Gay- Berne and multipoles. The new model has been applied to molecular dynamic simulations of neat methanol liquid. By placing a single point multipole at the oxygen atom rather than at the center of mass of methanol, there is a significant improvement in the ability to capture hydrogen- bonding. The critical issue of transferability of the coarse- grained model is verified on methanol - water mixtures, using parameters derived from neat liquids without any modification. The mixture density and internal energy from coarse- grained molecular dynamics simulations show good agreement with experimental measurements, on a par with what has been obtained from more detailed atomic models. By mapping the dynamics trajectory from the coarse- grained simulation into the all- atom counterpart, we are able to investigate atomic- level structure and interaction. Atomic radial distribution functions of neat methanol, neat water and mixtures compare favorably to experimental measurements. Furthermore, hydrogen- bonded 6- and 7- molecule chains of water and methanol observed in the mixture are in agreement with previous atomic simulations.