Influence of the complete basis set approximation, tight weighted‐core, and diffuse functions on the DLPNO‐CCSD ( T1 ) atomization energies of neutral H,C,O‐compounds

The impact of complete basis set extrapolation schemes (CBS), diffuse functions, and tight weighted‐core functions on enthalpies of formation predicted via the DLPNO‐CCSD(T1) reduced Feller‐Peterson‐Dixon approach has been examined for neutral H,C,O‐compounds. All tested three‐point (TZ/QZ/5Z) extrapolation schemes result in mean unsigned deviation (MUD) below 2 kJ mol⁻¹ relative to the experiment. The two‐point QZ/5Z and TZ/QZ CBS extrapolation schemes are inferior to their inverse power counterpart () by 1.3 and 4.3 kJ mol⁻¹. The CBS extrapolated frozen core atomization energies are insensitive (within 1 kJ mol⁻¹) to augmentation of the basis set with tight weighted core functions. The core‐valence correlation effects converge already at triple‐ζ, although double‐ζ/triple‐ζ CBS extrapolation performs better and is recommended. The effect of diffuse function augmentation converges slowly, and cannot be reproduced with double‐ ζ or triple‐ ζ calculations as these are plagued with basis set superposition and incompleteness errors.