Equilibrium molecular energies used to obtain molecular dissociation   energies and heats of formation within the bond-order correlation approach
  Ab initio calculations including electron correlation are still extremely costly except for the smallest atoms and molecules. Therefore, our purpose in the present study is to employ a bond-order correlation approach to obtain, via equilibrium molecular energies, molecular dissociation energies and heats of formation for some 20 molecules containing C, H, and O atoms, with a maximum number of electrons around 40. Finally, basis set choice is shown to be important in the proposed procedure to include electron correlation effects in determining thermodynamic properties. With the optimum choice of basis set, the average percentage error for some 20 molecules is approximately 20% for heats of formation. For molecular dissociation energies the average error is much smaller: ~0.4. 
A. Grassi, G. M. Lombardo, G. Forte, G. G. N. Angilella, R. Pucci, N.   H. March