Simple energy corrections for precise atomization energies of CHON molecules.

We test a few ways to improve atomization energies of CHON molecules and found that the best way to do it is simply by correcting the atom energies of the participating atoms. Extraordinary improvement on the average errors is obtained. For the HF/6-31G** level of theory an average error of 271.2 kcal/mol on 115 molecules is improved to 6.7 kcal/mol simply by correcting the atomic energy of the four chon atoms. The corrections to density functional methods allow us to reach a chemical accuracy of 2 kcal/mol.