A systematic study of water models for molecular simulation: Derivation of water models optimized for use with a reaction field

We have performed long molecular dynamics simulations of water using four popular water models, namely simple point charge ~SPC!, extended simple point charge ~SPC/E!, and the three point ~TIP3P! and four point ~TIP4P! transferable intermolecular potentials. System sizes of 216 and 820 molecules were used to study the dependence of properties on the system size. All systems were simulated at 300 K with and without reaction fields and with two different cutoff radii, in order to study the impact of the cutoff treatment on density, energy, dynamic, and dielectric properties. Furthermore we generated two special-purpose water models based on the SPC and TIP4P models, for use with a reaction field. The atomic charges and the Lennard-Jones C12 parameter were optimized to reproduce the correct energy and pressure using the weak coupling algorithm for parameters. Indeed, in simulations without parameter coupling of both new models the density and potential energy were found to be close to the experimental values. The other properties of these models that we called SPC/RF and TIP4P/RF ~where RF stands for reaction field! are evaluated and discussed. © 1998 American Institute of Physics. @S0021-9606~98!51317-7#