for the UEG in the low-density limit, the limit where w λ=1 (r) tends to w λ→∞ (r)). We can also see from the left panel of Fig. that the σλ→∞ (r) from the shell model is not a very good approximation to its 'exact' counterpart (that is σλ→∞ (r) obtained from the reference w λ→∞ (r) by rm-MRF). Nevertheless, w λ→∞ (r) from the shell model is highly accurate (see the right panel of Fig. ). This shows that one has some margin for error when modeling the MRF's fluctuation function, as the errors in the resulting XC energy densities are typically smaller than the errors in the fluctuation function. To further reinforce this point and since σλ→∞ (r) is on average around 1/2, we investigate here the MRF model where σλ→∞ (r) is simply always set to always to 1/2 ('MRF-half'). The resulting MRF-half w λ→∞ (r) for the beryllium atom is shown in the right panel of Fig. and compared against its reference and shell model counterpart. We can see that the resulting MRF-half approximation displays point-wise accuracy very similar to the shell model, which is, as said, the most accurate approximation to w λ→∞ (r) so far. Furthermore, MRF-half is even more accurate than the shell-model at larger distances from the nucleus (see the inset in the right panel of Fig. ).