Five individual parameters were optimized: two weight parameters w O and w H that control the molecular geometry, the charge on hydrogen q H , and the Lennard-Jones parameters for oxygen σ LJ and LJ . In order to optimize the geometry of the rigid water model, all interactions are defined in terms of off-center interaction sites (virtual sites) whose positions r O , r H1 , r H2 are defined in terms of the rigid TIP3P molecular geometry r O , r H1 , r H2 and the weight parameters w O and w H as: