Attempting to optimize new f-and g-type exponents while keeping the existing exponents fixed resulted in functions that were too diffuse to be effective in reducing the density fitting error; in most cases the additional exponents led to an increase in ∆DF. Adding an additional f-and g-type exponent, and then re-optimizing all of the f-and g-exponents for diatomic hydrides instead proved to reduce both δ EX and ∆DF to negligible values, with the largest exponents being significantly tighter than those when only the tightest exponents were optimized.