Structural,electronic, and optical absorption properties of TiO2 nanotube adsorbed with Cu n clusters

The structural, electronic, and optical absorption properties of TiO₂ nanotube (TiO₂NT) with Cu _n clusters (n =1–4) adsorbed on its surface have been investigated based on density functional theory calculations. The TiO₂NT is constructed by rolling up a (101) sheet of anatase TiO₂ around the \(\bar 101]\) direction; the ground states of Cu_n/TiO₂NT systems are determined by analyzing the average adsorption energies. Calculation results show that odd-even oscillations occur for the average adsorption energy, the Cu-O bond length, and the amount of transferred electrons, with the increase in Cu _n cluster size; and the Cu _n /TiO₂NTs with odd n’s demonstrate stronger interaction between the Cu _n cluster and the TiO₂NT. Also, the impurity states introduced by the Cu _n cluster to the band gap of TiO₂NT cause an obvious redshift of the optical absorption spectrum toward the visible light region, especially for the even n cases.