Gaussian-2 theory, Na+, and HF: a cautionary tale

The Gaussian-2 (G2) theoretical procedure delivers a sodium cation affinity (SCA) for HF of −119.1 kJ mol−1. In contrast, SCA values for NH3, H2O, PH3, H2S, and HCl are all positive according to G2 theory. Here we show that the negative SCA(HF) value delivered by G2 indicates a shortcoming in the electron correlation for metal atoms in frozen-core calculations on highly polar cations. Using a modified technique, denoted `G2(thaw)ʹ, we obtain a value of E0(NaFH+)=−262.03453 hartree, which yields the quantities ΔHf,0o(NaFH+)=255.2 kJ mol−1, SCA(HF)=66.8 kJ mol−1, and PA(NaF)=975.2 kJ mol−1.