Accurate molecular energies by extrapolation of atomic energies using an analytic quantum mechanical model

Using an analytic quantum-mechanical method based on Slater's X alpha method, we show that a fairly accurate estimate of the total energy of a molecule can be obtained from the exact energies of its constituent atoms. The mean absolute error in the total energies thus determined for the G2 set of 56 molecules is about 16 kcal/mol, comparable to or better than some popular pure and hybrid density functional models.