The exponents of the augmenting diffuse functions were determined by optimizing the MP2-F12 energy for the lowest electronic state of the atomic anions, using the Nelder-Mead simplex algorithm in Molpro's general purpose optimizer. In terms of ABSs, these optimizations used the large even-tempered (18s17p15d12f10g8h7i) "reference" sets described in Ref. as both MP2Fit and RI bases. All of the F12 calculations using diffuse augmented orbital basis sets use a modified version of the def2-QZVPP-JKFit ABS of Weigend in the density fitting of the exchange and Coulomb integrals. The modification takes the form of a single additional diffuse exponent added to each angular symmetry in an even-tempered fashion. The resulting ABS is known as def2-AQZVPP-JKFit in the Molpro basis set library.