Modeling diffusive dynamics in adaptive resolution simulation of liquid water.

We present a dual-resolution molecular dynamics (MD) simulation of liquid water employing a recently introduced Adaptive Resolution Scheme (AdResS). The spatially adaptive molecular resolution procedure allows for changing from a coarse-grained to an all-atom representation and vice versa on-the-fly. In order to find the most appropriate coarse-grained water model to be employed with AdResS, we first study the accuracy of different coarse-grained water models in reproducing the structural properties of the all-atom system. Typically, coarse-grained molecular models have a higher diffusion constant than the corresponding all-atom models due to the reduction in degrees of freedom (DOFs) upon coarse-graining that eliminates the fluctuating forces associated with those integrated-out molecular DOFs. Here, we introduce the methodology to obtain the same diffusional dynamics across different resolutions. We show that this approach leads to the correct description of the here relevant structural, thermodynamical, and dynamical properties, i.e., radial distribution functions, pressure, temperature, and diffusion, of liquid water at ambient conditions.