  Accurate predictions of material properties within the chemical space of
transition metal fluorides (TMFs), using density functional theory (DFT) is
important for advancing several technological applications. The
state-of-the-art semi-local exchange-correlation functionals within DFT include
the strongly constrained and appropriately normed (SCAN) and the restored
regularized SCAN (r$^2$SCAN), both of which are meta generalized gradient
approximation (metaGGA) functionals. Both SCAN and r$^2$SCAN are susceptible to
self-interaction errors (SIEs) while modelling correlated $d$ electrons of
transition metals. Hence, in this work, we evaluate the accuracy of both
functionals in estimating properties of TMFs, including redox enthalpies,
lattice geometries, on-site magnetic moments, and band gaps. We observe both
SCAN and r$^2$SCAN to exhibit poor accuracy in estimating fluorination
enthalpies among TMFs, attributable to SIEs among the $d$ electrons. Thus, we
derive optimal Hubbard $U$ corrections for both functionals based on
experimental fluorination enthalpies of binary TMFs. Note that the linear
response theory yielded unphysical $U$ values for V, Fe, and Ni fluorides.
While adding the optimal $U$ to the metaGGA functionals does not significantly
affect the lattice volumes and magnetic moments, it does significantly increase
the calculated band gaps. Also, we calculate the average Na intercalation
voltage in Mn, Fe, Co, and Ni fluorides as a transferability check of our
optimal $U$ values. Overall, we recommend using the Hubbard $U$ correction to
improve predictions of redox enthalpies in other TMFs, while for band gap
predictions, we suggest using the non-corrected functionals. Finally, our study
should advance the accuracy of DFT-based screening studies to unearth novel
TMFs, which can be used in various applications, including energy storage,
catalysis, and magnetic devices.
