High-level ab initio calculations have been used to determine the binding energy of F(H2O)(-). A value of -27.3 kcal/mol has been obtained, which is considerably greater than the experimental value near -23 kcal/mol. The new theoretical value is used to parametrize a hybrid quantum mechanical (QM)/molecular mechanical (MM) potential in which F- is described at a high level of quantum mechanics and H2O is modeled with a fluctuating charge MM potential. Static and dynamic calculations of F(H2O)(4)(-) are carried out using this hybrid QM/MM potential. Static calculations using both full electronic structure methods and the hybrid potential predict a range of interior and surface structures within 2 kcal/mol, while molecular dynamics simulation at 300 K using the hybrid potential suggests that a range of structures will be observed.