Comparison between models K2 (gray dashed line) and K2-MZvar (blue solid line) with A₂ = 0.12. Left panel: metallicity profile in the interior of present-day Sun. Right panel: time evolution of the surface metallicity Z_surf. The gray vertical lines denote M₁(= 0.904 M_⊙), M₂(= 0.962 M_⊙), and the end of the accretion phase for model K2-MZvar. The target value of Z_surf at 4.567 Gyr is 0.0134 ± 0.0007 (see Table 3).