The ligand effect on the isomer stability of Au24(SR)20 clusters

A key challenge in nanocluster research in particular and nanoscience in general is structure prediction for known compositions. Usually a simple ligand such as a methyl group is used to replace complex ligands in structure prediction of ligand-protected nanoclusters. However, how ligands dictate the energy landscape of such a cluster remains unclear. Here we elucidate the role of the ligand effect on the isomer stability of Au-24(SR)(20) nanoclusters by computing the relative energy of two isomers (one from the experiment, denoted as the J isomer; the other is the best theoretical model, denoted as the P isomer) of Au-24(SR)(20) with dispersion-corrected density functional theory. We find that when R = -CH3, the two isomers are equally stable (within 0.13 eV), but for R = -CH2CH2Ph the P isomer is more stable by 1.6 eV and for R = -CH2Ph-Bu-t the J isomer is more stable by 1.0 eV. Partition of the total energy into DFT and vdW contributions indicates that the higher stability of the P isomer in the case of R = -CH2CH2Ph stems from the stronger vdW interactions among -CH2CH2Ph groups, while the higher stability of the J isomer in the case of R = -CH2Ph-Bu-t is due to its better capacity to respond to the steric effect of the larger -CH2Ph-Bu-t groups. This finding confirms that the ligand plays a crucial role in dictating the isomer stability.