  Calcium batteries (CBs) are potential next-generation energy storage devices,
offering a promising alternative to lithium-ion batteries due to their
theoretically high energy density, better safety, and lower costs associated
with the natural abundance of calcium. However, the limited availability of
positive electrode (cathode) materials has constrained the development of CBs
so far. Given the similar ionic radii of Na$^+$ and Ca$^{2+}$, structures that
are effective at reversibly intercalating Na$^+$ may be able to reversibly
intercalate Ca$^{2+}$ as well. In this context, transition metal fluorides
(TMFs) exhibiting weberite and perovskite structures that are known for
intercalating Na$^+$ form an interesting set of possible CB cathode frameworks.
Thus, we use first principles calculations to explore weberite and perovskite
TMFs as CB cathodes, of compositions
Ca\textsubscript{x}M\textsubscript{2}F\textsubscript{7} and
Ca\textsubscrpt{x}MF\textsubscript{3}, respectively, where M = Ti, V, Cr, Mn,
Fe, Co, or Ni. We systematically evaluate key cathode properties, including
ground state structure, average Ca-intercalation voltage, thermodynamic
stability (at 0 K), theoretical capacity, and Ca$^{2+}$ migration barriers.
Importantly, we identify
Ca\textsubscript{x}Cr\textsubscript{2}F\textsubscript{7} and
Ca\textsubscript{x}Mn\textsubscript{2}F\textsubscript{7} weberite frameworks as
promising Ca-cathodes. Our study not only unveils potential CB cathodes but
also paves the way for further advancement in TMF-based intercalation cathodes,
diversifying the chemical space for next-generation energy storage systems.
