Ground-state enthalpies: evaluation of electronic structure approaches with emphasis on the density functional method.
Ground-state enthalpies, calculated by various electronic structure methods, are compared with experimentally well-established values across a sizable data base 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 DAtEF (Data base optimized Atomic Enthalpies of Formation) 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 approximately 20 kJ/mol rms (approximately 4.8 kcal/mol). This must be considered an excellent result, as presently only the heaviest available methods appear to provide about a factor of 2 more accuracy as inferred from a subset of the data base used here.
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Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.