Accurate Gas Phase Formation Enthalpies of Alloys and Refractories Decomposition Products

Accurate gas phase formation enthalpies, ΔH_f, of metal oxides and halides are critical for the prediction of the stability of high temperature materials used in the aerospace and nuclear industries. Unfortunately, the experimental ΔH_f values of these compounds in the most used databases, such as the NIST-JANAF database, are often reported with large inaccuracy, while some other ΔH_f values clearly differ from the value predicted by CCSD(T) methods. To address this point, in this work we systematically predicted the ΔH_f values of a series of these compounds having a group 4, 6, or 14 metal. The ΔH_f values in question were derived within a composite Feller-Dixon-Peterson (FDP) scheme based protocol that combines the DLPNO-CCSD(T) enthalpy of ad hoc designed reactions and the experimental ΔH_f values of few reference complexes. In agreement with other theoretical studies, we predict the ΔH_f values for TiOCl₂, TiOF₂, GeF₂, and SnF₄ to be significantly different from the values tabulated in NIST-JANAF and other sources, which suggests that the tabulated experimental values are inaccurate. Similarly, the predicted ΔH_f values for HfCl₂, HfBr₂, HfI₂, MoOF₄, MoCl₆, WOF₄, WOCl₄, GeO₂, SnO₂, PbBr₄, PbI₄, and PbO₂ also clearly differ from the tabulated experimental values, again suggesting large inaccuracy in the experimental values. In the case when largely different experimental values are available, we point to the value that is in better agreement with our results. We expect the ΔH_f values reported in this work to be quite accurate, and thus, they might be used in thermodynamic calculations, because the effects from core correlation, relativistic effects, and basis set incompleteness were included in the DLPNO-CCSD(T) calculations. T1 and T2 values were thoroughly monitored as indicators of the quality of the reference Hartree-Fock orbitals (T1) and potential multireference character of the systems (T2).