Intrinsic Chirality in Bare Gold Nanoclusters: The AU34- Case

In this work, we provide theoretical evidence on the existence of energetically stable chiral structures for bare gold clusters. Density functional theory calculations within the generalized-gradient approximation were performed to systematically study structural, vibrational, electronic, and optical properties of the lowest-lying isomers of the AU(34)(Z), (Z = +1, 0, -1), Clusters. Our results show that for the neutral and charged clusters, the lowest-energy isomer hash a C, (chiral) structure. In addition, a C-3 (chiral) isomer was found nearly degenerate in energy with the C, isomer. These results are in agreement with previous theoretical-experimental studies done for the AU(34)(-) cluster; however, because our calculated molecular scattering functions for the C-1 and C-3 isomers of this cluster are almost indistinguishable, it is concluded that the actual resolution in trapped ion electron diffraction experiments is not enough to discriminate between them. On the other hand, the electronic density of states of the C, isomer shows better overall agreement with the measured photoelectron spectrum of the AU(34)- cluster than that one corresponding to the C-3 isomer. The electronic density of states of these isomers also shows different features in the energy region of the HOMO-LUMO gap, which would generate distinct behavior in their optical properties. In fact, the calculated absorption and circular dichroism spectra of the two chiral isomers show clear differences in their line shape. Another important property that distinguishes the C-1 and C-3 isomers is the different spatial distribution of the atomic coordination on the cluster surface. Our results confirm that the potential energy surface of bare gold clusters could have lowest-lying energy minima corresponding to intrinsically chiral structures.