The SF6− enigma for density functional theory: is the KMLYP functional a reasonable solution for this problematic anion?

The adiabatic electron affinity (EA) of sulfur hexafluoride (SF6) was determined using six different density functional or hybrid Hartree–Fock/density functional methods, including the recently developed KMLYP functional. With the extensively calibrated DZP++ basis set, the KMLYP functional predicts an EA for SF6 of 1.48 eV. This value is in better agreement with experiment (1.07 ± 0.01 eV) than the best previously established DFT method (BHLYP, 1.69 eV) for related systems. The other four functional give electron affinities of 2.66 (B3LYP), 2.83 (B3P86), 3.22 (BLYP), and 3.00 eV (BP86). However, the difference from the experimental value is still about twice a large as DFT is usually able to obtain.