Force field parametrization by weak coupling. Re-engineering SPC water

A recently developed scheme for the automatic adjustment of force field parameters to experimentally observed properties is applied to the simple-point-charge (SPC) water model. The refinement procedure is based on a first-order coupling of a force-field parameter (say, an atomic charge) to the deviation of a calculated bulk liquid property (e.g. the heat of vaporization) from its ideal value. I.e. the method is very similar in spirit to the weak-coupling scheme used to implement constant-temperature or constant-pressure molecular dynamics. With the method we have refined the charges and the Lennard-Jones diameter of the SPC water model at several state points of high temperature and high pressure. We also have studied how these force-field parameters have to be reoptimized as the cutoff distance is varied.