(3.3.14) Neese : It appears to me that "sufficient accuracy" is something that depends largely on the context of the computational problem at hand. Take a very exothermic reaction, with a free-energy change of around -50 kcal/mol. I don't think I would understand anything about this reaction any better whether I compute the energy change to be -47 or -53 kcal/mol, nor would it change any conclusion. On the other hand, if one wants to correctly predict the enantiomeric excess of a bifurcating reaction that may lead to different stereochemical outcomes, then even one half of a kcal/mol matters.