In their 2023 article [Phys. Rev. Mater. 7, 075401 (2023)], Adhikari et al. predicted “excellent phase stability against decomposition” for all 12 ${\mathrm{Cs}}_{2}M\mathrm{Sb}{X}_6$ ($M=\mathrm{Cu}$, Ag, Na, K, Rb, Cs; $X=\mathrm{Cl}$, Br) halide double perovskites (HDPs). However, this optimistic claim relied on decomposition pathways limited to binary products, neglecting critical ternary competing phases. By rigorously incorporating all possible decomposition routes with experimentally validated structures, we demonstrate that only ${\mathrm{Cs}}_2{\mathrm{AgSbCl}}_6$ ($\mathrm{\Delta }{H}_{\mathrm{d}}=3.9$ meV/atom) and ${\mathrm{Cs}}_2{\mathrm{NaSbCl}}_6$ ($\mathrm{\Delta }{H}_{\mathrm{d}}=1.8$ meV/atom) are thermodynamically stable, while the remaining 10 HDPs are either marginally metastable (for ${\mathrm{Cs}}_2{\mathrm{AgSbBr}}_6, \mathrm{\Delta }{H}_{\mathrm{d}}=-2.6$ meV/atom) or intrinsically unstable. Notably, Cu(I)-based systems—such as ${\mathrm{Cs}}_2{\mathrm{CuSbCl}}_6$ and ${\mathrm{Cs}}_2{\mathrm{CuSbBr}}_6$ ($\mathrm{\Delta }{H}_{\mathrm{d}}=-37.6$ and −40.1 meV/atom)—exhibit severe instability due to Cu(I)'s inherent aversion to octahedral coordination, a key destabilizing mechanism previously overlooked. These results reconcile computational predictions with experimental synthesis feasibility, resolving long-standing discrepancies. This Comment underscores the necessity of modeling realistic competing phases and comprehensive decomposition thermodynamics in stability assessments of emerging multicomponent materials, challenging oversimplified approaches in materials design.

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• Electronic structure
• Energy applications
• Energy harvesting devices
• Energy materials
• First-principles calculations
• Solar energy
• Thermodynamics
• Hybrid perovskites