Electronic structure and optical transitions of Au(20-x)Cu(x) nanoclusters.

Gold nanoclusters are promising for photothermal therapy, radiotherapy and cancer cell imaging. We have performed a first-principles study to evaluate the electronic and optical properties of Au7, Au13, Au19, Au20, and Au(20-x)Cu(x) clusters. We have employed the Perdew-Burke-Ernzerhof form of generalized gradient approximation in the frame work of density functional theory. Calculations have been carried out in different configurations. With increasing Cu atoms, the HOMO-LUMO gap of Au(20-x)Cu(x) clusters is decreased due to the increase of electronic states in the HOMO. The results of imaginary part of the dielectric function indicate that the optical transition between HOMO and LUMO has shifted to the low energy range as the Cu atoms increase. The Au and Au(20-x)Cu(x) clusters show tunable optical properties.