Conformational energies of microsolvated Na ⁺ clusters with protic and aprotic solvents from GFN n ‐xTB methods

Performance of contemporary tight‐binding semiempirical GFNn‐xTB methods for the conformational energies of singly charged sodium clusters Na⁺(S)_n (n = 4–8) with 3 protic and 8 aprotic solvents is examined against the reference RI‐MP2/CBS method. The median Pearson correlation coefficients of ρ = 0.84 (GFN2‐xTB) and ρ = 0.82 (GFN1‐xTB) do not give the clear preference to any tested approach. GFN1‐xTB method demonstrates more stable performance than its GFN2‐xTB successor with the average mean absolute errors (MAEs)/mean signed errors (MSEs) of 1.2/0.2 and 2.3/1.6 kcal mol⁻¹, respectively. Conformational energies produced by the computationally efficient DFT functional PBE and double‐ζ basis set complemented with –D3(BJ) dispersion correction are suitable for the preliminary sampling (median ρ = 0.93), but should be used with a caution for the calculations of the average ensemble properties (MAE/MSE = 1.7/1.1 kcal mol⁻¹). Higher‐ranking PBE0‐D3(BJ) and ωB97M‐V with triple‐ζ basis sets yield significantly lower MAEs/MSEs of 0.55/0.20 and 0.51/0.23 kcal mol⁻¹, respectively.