results discontinuities in the IRC potential energy curve, which can be made much smoother by including more electronic states, like 5-state-SA-CASSCF. However, artificial non-degeneracies were introduced in both reactant and product asymptotes with equal weightings for all states in the CASSCF calculations. Finally, the dynamically weighted SA-CASSCF (DW-SA-CASSCF) calculation was proposed to eliminate the discontinuities and the artificial nondegeneracies. Indeed, the MRCI calculation, followed by 5-state-DW-SA-CASSCF computation, was used to develop the first full-dimensional ab initio based PESs for reactions F/Cl + H2O → HF/HCl + OH. As expected, the near triple degeneracy is clearly shown in the pre-reaction well (F…H2O or Cl…H2O)