Size evolution study on the electronic and optical properties of gold-cluster complexes Au₄-S-C_nH_2n-S^″-Au₄^″ (n = 2–5)

Relativistic unrestricted time-dependent density functional theory calculations were performed for obtaining the absorption spectra of gold-cluster complexes Au₄-S-C_nH_2n-S^′-Au₄^′ (n = 2–5). The range-separated exchange-correlation functional CAMYB3LYP was used to properly predict charge transfer excitations. The absorption UV–vis spectrum is not affected by size if structure and metal-molecule bonding remains similar. Changes in the ‘local’ structure and bonding have drastic effects on these systems’ electronic transitions. The HOMO-LUMO gap of the cluster complexes shows a zig-zag behavior typical of gold nanoclusters with respect to the size of the alkanedithiol chain (n).