The Accuracy of calculated electronic ground state energies

Ground-state enthalpies, calculated by a wide variety of electronic structure methods, are compared with experimentally well established values across a sizable database of 577 molecules and 15 atoms. With the diversity of species and bonding types available in this compilation it is possible to detect deficiencies that may escape with smaller test sets. The present analysis relying on ``Database optimized Atomic Enthalpies of Formation'' (DAtEF) yields error statistics which relate to reaction enthalpies among the species much more directly than extrapolations based on atomization enthalpies. The evaluation is applied to methods ranging from high level first principles wavefunction calculations to density functionals and to semiempirical approaches. It is found that computationally efficient and broadly applicable density functional methods with relatively small but adequate numerical basis sets can provide ground state enthalpies within $\approx$ 20 kJ/mol RMS ( $\approx$ 4.8 kcal/mol). This must be considered an excellent result, as presently only the heaviest available methods may provide about a factor of 2 more accuracy, if the conclusions inferred from a subset of the database hold up.