Elaborated thermochemical treatment of HF, CO, N2, and H2O: Insight into HEAT and its extensions

Empirical, highly accurate non-relativistic electronic total atomization energies (eTAEs) are established by combining experimental or computationally converged treatments of the nuclear motion and relativistic contributions with the total atomization energies of HF, CO, N-2, and H2O obtained from the Active Thermochemical Tables. These eTAEs, which have estimated (2 sigma) uncertainties of less than 10 cm(-1) (0.12 kJ mol(-1)), form the basis for an analysis of high-level ab initio quantum chemical calculations that aim at reproducing these eTAEs for the title molecules. The results are then employed to analyze the performance of the high-accuracy extrapolated ab initio thermochemistry, or High-Accuracy Extrapolated Ab Initio Thermochemistry (HEAT), family of theoretical methods. The method known as HEAT-345(Q), in particular, is found to benefit from fortuitous error cancellation between its treatment of the zero-point energy, extrapolation errors in the Hartree-Fock and coupled cluster contributions, neglect of post-(T) core-correlation, and the basis-set error involved in higher-level correlation corrections. In addition to shedding light on a longstanding curiosity of the HEAT protocol-where the cheapest HEAT-345(Q) performs comparably to the theoretically more complete HEAT-456QP procedure-this study lays the foundation for extended HEAT variants that offer substantial improvements in accuracy relative to the established approaches.

Automated summary

This study establishes empirical, highly accurate non-relativistic electronic total atomization energies and analyzes the performance of high-level ab initio quantum chemical calculations and the HEAT family of theoretical methods. The results show that the HEAT-345(Q) method benefits from fortuitous error cancellation and lays the foundation for extended HEAT variants with substantial improvements in accuracy.