FORCE-FIELD PARAMETRIZATION BY WEAK-COUPLING - REENGINEERING SPC WATER

A recently developed scheme for the automatic adjustment of force fiel d parameters to experimentally observed properties is applied to the s imple-point-charge (SPC) water model. The refinement procedure is base d 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. t he heat of vaporization) from its ideal value. I.e. the method is very similar in spirit to the weak-coupling scheme used to implement const ant-temperature or constant-pressure molecular dynamics. With the meth od we have refined the charges and the Lennard-Jones diameter of the S PC water model at several state points of high temperature and high pr essure. We also have studied how these force-field parameters have to be reoptimized as the cutoff distance is varied.