On the additivity of basis set effects in some simple fluorine containing systems

Abstract

AbstractThe reactions F + H2 → HF + H, HF → H + F, F → F+ + e− and F + e− → F− were used as simple test cases to assess the additivity of basis set effects on reaction energetics computed at the MP4 level. The 6‐31G and 6‐311G basis sets were augmented with 1, 2, and 3 sets of polarization functions, higher angular momentum polarization functions, and diffuse functions (27 basis sets from 6‐31Gd, p) to 6‐31 ++ G(3df, 3pd) and likewise for the 6‐311G series). For both series substantial nonadditivity was found between diffuse functions on the heavy atom and multiple polarization functions (e.g., 6‐31 + G(3d, 3p) vs. 6‐31 + G(d, p) and 6‐31G(3d, 3p)). For the 6‐311G series there is an extra nonadditivity between d functions on hydrogen and multiple polarization functions. Provided that these interactions are taken into account, the remaining basis set effects are additive to within ±0.5 kcal/mol for the reactions considered. Large basis set MP4 calculations can also be estimated to within ±0.5 kcal/mol using MP2 calculations, est. EMP4(6‐31 ++ G(3df, 3pd)) ≈ EMP4(6‐31G(d, p)) + EMP2(6‐31 ++ G(3df, 3pd)) – EMP2(6‐31G(d, p)) or EMP4(6‐31 + G(d, p) + EMP2(6‐31 ++ G(3df, 3pd)) – EMP2(6‐31 + G(d, p)) and likewise for the 6‐311G series.