Global fit of ab initio potential energy surfaces: II.2. Tetratomic systems A2B2 and ABC2 Original Research Article

Global potential energy surfaces (GPES) for tetratomic molecular systems, containing at least one group of two identical nuclei, which fit ab initio data can be obtained preserving the accuracy of the ab initio points. The permutational symmetry of the potential, corresponding to the two identical nuclei, is treated analytically in this new version of the previous published program GFIT4C (Computer Physics Communications catalogue number: ADNB). The global fit obtained fulfills the stringent criteria needed for molecular dynamical calculations. The program writes out as output file a Fortran-77 program in a form such that the potential and its derivatives with respect to coordinates can be evaluated readily and accurately at arbitrary geometries.