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 $16\mathrm{kcal}∕\mathrm{mol}$, comparable to or better than some popular pure and hybrid density functional models.