2.

(a) Planar average charge density difference (CDD) along the surface normal for the Cu₂O {100} surface decorated with a 4-BA molecule and the side view in the 3D representations (upper panel). The oblique view of the CDD for the Cu₂O {100} surface decorated with 4-BA molecules (lower panel). The isosurface value is set to 0.001 e/Bohr³. The purple and gray regions represent charge accumulation and depletion, respectively. Band structure of (b) the pristine Cu₂O {100} surface and (c) decorated with a 4-BA molecule. The band-decomposed charge density of the (d) higher (denoted as 1) and (e) lower (denoted as 2) 4-BA-induced band within the band gap for the {100} surface. The orange lines are Fermi level, which are all aligned to zero. (f) Planar average electrostatic potential along the surface normal for the Cu₂O {100} surface decorated with a 4-BA molecule. The red and blue solid lines are denoted as vacuum level and Fermi level, respectively. The yellow dashed line represents the average potential of the decorating molecule.