Optimizing a transition state

Pick a reaction coordinate involving bonds breaking and forming. First assume symmetric changes in bond distances. A Force1 of 500 and Force2 of 1.000 is a good start for a constraint. Gradually weaken the constraints to see if the barrier will be lowered, while retaining a reasonable shape of the curve. A Force2 constraint of 0.250 seems to work well in this lowering. Run low temperature MD with the variable distance restraint.

Once the curve has been generated, go to the geometry at the top of the barrier. Keep the constraints on. Don't forget to zero out the variable parameter for changing the distances. Run a low temperature MD to relax the structure to see if a lower energy structure can be found.

If successful, then starting from this point march down the hill in both directions to make sure this leads to both reactants and products. Then pick the barrier top and 1-2 points close to it on either side, and also the reactants and products and minimize these structures. So if you had: barrier top, 2 close structures on either side, the reactant and the product, that would be seven structures. Use these to generate an energy curve and stick this into the training set.