We used a genetic algorithm to fit a set of energy differences obtained by neglect-of-diatomic-differential-overlap (NDDO) molecular orbital theory to reference ab initio data, yielding a set of specific reaction parameters (SRP) for the reaction Cl + CH4. Only a small number ab initio points along a distinguished-coordinate path were used as input, but the surface is well fit both on and off the reaction path over a range of energies three times wider than the input range. The resulting NDDO-SRP potential energy surface is almost four orders of magnitude less expensive to evaluate than the reference ab initio surface and is well suited for direct dynamics calculations.
Bibliographical noteFunding Information:
This work is supportedin part by the US Department of Energy, Office of Basic Energy Sciences (variational transition state theory) and by NASA (high-energyc hemicald ynamics).