A NEW FUNCTIONAL FORM TO OBTAIN ANALYTICAL POTENTIALS OF TRIATOMIC-MOLECULES

A new way of fitting ab initio values of the potential energy of triatomic molecules is discussed. The new functional form proposed for the potential energy function satisfies several criteria for use in scattering calculations and it is so stable that, when increasing the number of parameters in the fit, it maintains a good behavior at short, intermediate, and long range of the whole potential. Applications of the fitting technique to obtain the potential energy functions for the ground states of H-3, H2He+, and LiHF are presented. For the H-3 system, we fit all 267 of Liu and Siegbahn's ab initio points. With one nonlinear parameter and 23 linear parameters, the root-mean-square error was 1.21 kcal/mol and the maximum absolute deviation 7.94 kcal/mol; these values are lower than previous global fittings with a similar number of parameters except for the Truhlar and Horowitz fit of the Liu and Siegbahn data, LSTH potential, but when the number of linear parameters was increased to 71, the root-mean-square error was reduced to 0.07 kcal/mol and the maximum absolute deviation to 0.25 kcal/mol (approximately one half the corresponding values of the LSTH ones). The new global fitting procedure is then applied to obtain potential energy functions for the H2He+ and the LiHF systems within the chemical accuracy of 1 kcal/mol.