Our values, derived from the independent-particle approximation, tend to overestimate the dielectric constants derived in QP (DFT) framework compared with experimental measurements for Ga 2 O 3 within the range ε ∞ = 3.2-3.7 and somewhat larger values of ε ∞ = 3.9-4.0, 9,99 or ε ∞ = 4.8 ± 0.02 for In 2 O 3 . When QP and excitonic effects are incorporated into the computation of the dielectric functions, the resulting QP electronic dielectric constants are reduced and align more closely with the experimental values. Another significant quantity derived from the frequency-dependent real parts is the set of frequencies where the condition Reε(ω) = 0 is met. We observe zeros in the ranges of hω = 14-16 eV (lower) and 21-24 eV (upper) for Ga 2 O 3 polymorphs, and 13-15 eV (lower) and 16-18 eV (upper) for In 2 O 3 phases, as shown in the zoomed-in panels on the right of Figs. 10 and 11. These zeros may nearly correspond to the energies of plasmonic excitations in the examined oxide polymorphs. Their reduced dependence on the group-III cation suggests that the main contributions to plasmonic excitations are due to the valence electrons in occupied O 2p bands. Furthermore, given the volumes per formula unit of approximately V 0 ≈ 50 Å 3 for Ga