Upper panel: inner chemical profiles of ¹⁶O, ¹²C, ⁴He and H, and the logarithm of the Rosseland opacity (κ) vs. the outer mass fraction coordinate, corresponding to a DA WD model with M_⋆ = 0.584 M_⊙, log(M_H/M_⋆) = − 11.8, and T_eff = 19 000 K. The H–He interface is shaped by element diffusion. The bumps in κ due to the second ionization of He and the ionization of H are evident. Lower panel: normalized differential work function corresponding to a stable g mode with k = 16 and period Π = 800 s.