THE REACTION FIELD METHOD IN MOLECULAR-DYNAMICS SIMULATIONS OF POINT-POLARIZABLE WATER MODELS

Models of liquid water have been studied that, while conceptually simp le, incorporate the contributions from both molecular polarizability a nd long-range interactions explicitly. The models use nuclei-centred p olarizable point-dipoles in conjunction with the reaction field method , assuming a rigid molecular geometry. In a molecular dynamics impleme ntation of such models, the presence of the reaction held term gives r ise to specific additional torques; these are most readily accounted f or by a force redistribution method, thus allowing for the use of stan dard constraint dynamics. It is found that determination of the 'true' induced polarization via iteration does not necessarily involve a lar ge computational overhead and hence constitutes a viable alternative t o the extended Lagrangian methods that imply internal molecular fluctu ations. As an example of this class of water models, the parametrizati on of simple three- and four-site models with an oxygen-centred isotro pic polarizability term has been considered. The results are compared with findings from other recent simulations of polarizable water and i llustrate some major trends concerning the effects of the precise spec ification of the model on structure, energetics and dynamics.