Turbulent diffusion coefficient (according to Eq. (5)) in a 1.7 M_⊙-model computed with TGEC at two evolutionary stages. The solid line represents the diffusion coefficient below the surface convective zone (due to the ionization of H and He) at 170 Myr, the dashed line represents the diffusion coefficient below the iron convective zone (assumed connected with the H and He ones) at 588 Myr, the vertical dotted line represents the base of the iron convective zone.