Schematic illustration showing the structure evolution (panel a; the so-called Kippenhahn diagram) and the D_mix profile at the solar age (panel b) of our fiducial model, K2-MZvar-TM (see Table 2). The convective zones are depicted as a cloudy region. The color of the shade in panel a shows Z_accretion. The two lines at the stellar surface and center illustrate metallicity by color. The two dashed green lines the locations at temperatures 2.5 × 10⁶ and 3.5 × 10⁶ K, indicative of Li and Be burning, respectively.