Size evolution relativistic DFT-QTAIM study on the gold cluster complexes Au₄-S-C_nH_2n-S″-Au₄″ (n = 2–5)

We introduce relativistic density functional theory (DFT) calculations on the gold cluster complexes (cluster-molecule-cluster) Au₄-S-C_nH₂n-S′-Au₄′ (n = 2–5). The structural, electronic and relativistic (ZORA) Bader's quantum theory of atoms in molecules (QTAIM) properties of the two lowest-energy complex isomers were computed as a function of the alkanedithiol size (n). The lowest-energy isomer is a triplet spin state independently of the complex size. According to QTAIM, the Au-Au and S-Au bonds are classified as closed shell (non-covalent) type. The HOMO-LUMO gap of the cluster complexes shows a zigzag behavior typical of gold nanoclusters with respect to the size of the alkanedithiol chain (n).