Reliable Quantum-Chemistry Heats of Formation for an Extensive Set of C-, H-, N-, O-, F-, S-, Cl-, Br-Containing Molecules in the NIST Chemistry Webbook.

Abstract

In the present study, we have computed the heat of formation (HOF) for over 500 C-, H-, N-, O-, F-, S-, Cl-, Br-containing molecules in the NIST Chemistry Webbook with a previously established methodology [from the highest- to lowest-level methods, W1X-2, CCSD(T)-F12b, DSD-PBEP86, and ωB97M-V, with the lower levels calibrated against higher levels for the atomic energies, see: J. Phys. Chem. A 2022, 126, 4981-4990]. We find a reasonable level of agreement between the computed and NIST values for the present set of species. However, the set of F-containing compounds shows considerably larger discrepancies, which can in part be attributed to dubious experimental values, as we have demonstrated in some cases. With our highest-level computed HOFs, we validated the lower-level methods used in our protocol. Specifically, CCSD(T)-F12b yields chemically accurate (±4.2 kJ mol^-1) values for all types of molecules, while DSD-PBEP86 and ωB97M-V yield similar levels of accuracy for most systems, with key exceptions being molecules with numerous electron-withdrawing F and NO₂ groups. Our results further support the use of the protocol for the computation of HOFs, particularly for systems with few reliable reference values.