directly with some kinetics from experiments that is not subject to all the varied assumptions made in order to obtain some sort of barrier height.
I think we should not get hung up on the issue of how to calibrate methods for calculating transition states and how to get error bars on the heights of barriers. We should go the next step further, integrate the dynamics into the calculation and then compute what the experimentalists actually measure and compare that with the experiment. That is the way to get reliable calibrations.
Thom Dunning: While there have not been many calculations, there have been some that would certainly indicate that the techniques that we currently have available to us can achieve very high accuracy. It does turn out that calculations of transition states are significantly more challenging than calculations of stable species. The basis sets you have to use are larger and you have to go much closer to convergence to get reliable numbers. But I would say that the best techniques can get errors on the order of tenths of a kilocalorie per mole. But for the few systems that have been checked, the problem there is, as John says, that we really do not have any good information from experiment that pertains directly to what we are calculating. We have to go to the step that Peter is talking about to be able to compare with experiments.