To develop cc-pVnZ/JKFit auxiliary sets for Na and Mg, optimizations were carried out on NaH and MgH + , respectively. Briefly, a common (13s11p9d) auxiliary basis 'kernel' was optimized for the cc-pV5Z orbital basis and used in all JKFit sets for these elements. Higher-angular momentum functions for TZ-5Z were optimized for the corresponding orbital basis, with the total composition of the resulting JKFit sets (see Table ) matching those of Weigend for the elements Al-Cl. Following the procedure adopted in the Molpro basis set library, 33 cc-pVDZ/JKFit sets for Na and Mg were generated by simply removing the g-type functions from cc-pVTZ/JKFit.