The structure of a thiolate-protected Au44 cluster, [Au44(SR)28], is theoretically predicted via density functional theory calculations. Au44(SR)28 is predicted to contain a "two-shell" face-centered-cubic type of Au kernel and possess chirality. The predicted cluster structure is validated by comparison of optical absorption properties between theory and previous experiments, as well as energy evaluations. Based on the predicted cluster structure, the magic stability of Au44(SR)28 is understood from the superatom electronic configuration and formation of a unique double-helix superatom network inside.

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Atomically precise thiolate-protected Au nanoclusters (NCs), i.e. Au m (SR) n , have attracted intensive research interest during the past few years. Recently, the synthesis and isolation of selenolate-protected gold clusters (Au m (SeR) n ) via the ligand exchange of thiolate with selenol were achieved, which demonstrated identical compositions to those of thiolate-protected Au NCs. In this study, we perform a comprehensive theoretical study on the structure, electronic structure, and electronic optical absorption properties of 11 selenolate-protected gold clusters on the basis of density functional theory (DFT) calculations. Our results propose that the selenolate-protected Au NCs with framework structure identical to the thiolated ones are stable local minima. The ligand effect is proposed to understand the distinct geometrical structures of Au24(SeR)20 and Au24(SR)20 NCs. In addition, the optical absorption properties of thiolate- and selenolate-protected Au NCs are compared via the time-dependent density functional theory (TD-DFT). The results indicate that two types of Au NCs possess similar shape of electronic optical absorption spectra and electronic structure. The excitation wavelength dependent intermolecular electron transfer between the Au25(ER)− (E = S and Se) and O2 is revealed as well.