Validation of a Database of Formation Enthalpies and of Mid-Level Model Chemistries

In order to test new procedures for the calculation of basic molecular properties, a properly validated database and computational method appropriate to the range of species at hand is essential. Here formation enthalpies of chemical species C_mH_nN_pO_q from their constituent atoms are computed by midlevel composite model chemistries in order to check the contents of the best established and most accurate database, ATcT. Once discrepancies are identified alternative independent procedures and/or higher level model chemistries, which include CCSDT(Q) calculations, are employed to resolve the problems. Shortcomings of the midlevel methods used are signaled where these occur. In addition a more visual statistical analysis than is usual is presented which highlights the outliers and identifies the bias of each method together with associated error bars and the 95% limits of agreement and its error bars.