A new rigid non-polarizable model for semi-heavy water: TIP4P/2005-SHW

In molecular dynamics (MD) simulations of water, rigid non-polarizable models are still valuable and widely used because of their low computational cost and excellent performance. Most of such models have been for light water (H2O) for a long time, and a few have recently been reported for heavy water (D2O). The specific models of D2O are needed because of its notably slower dynamics and stronger hydrogen bond than H2O. To our knowledge, no models of semi-heavy water (HOD) were made, although HOD is the most abundant and, therefore, most important chemical species in isotopically diluted water (IDW) prepared by mixing equal amounts of H2O and D2O. For precise MD simulations of IDW, a specific model of HOD is definitely needed. Here, we report the development of a new rigid non-polarizable model of HOD, TIP4P/2005-SHW, on the basis of the most popular H2O model, TIP4P/2005, and its D2O counterpart, TIP4P/2005-HW. We show the details of the development and demonstrate the high reproducibility of TIP4P/2005-SHW in terms of the density, the temperature of maximum density, the viscosity, and the diffusion coefficient.