Basis set dependence of ab initio geometry predictions for AB4 molecules

Theoretical predictions of AB₄ molecular structures are very sensitive to choice of basis set. This has been previously demonstrated for the SH₄ and SF₄ molecules. Here it is shown that while both minimum and double zeta basis sets predict ClF₄⁺ to have a C_4v structure, the addition of d functions on Cl results in a C_2v geometry, similar to the experimentally known structure of SF₄.