Performance of Density Functionals and Semiempirical 3c Methods for Small Gold-Thiolate Clusters Au3(SMe)3

We present a performance study on popular density functionals (DFAs) and three-part corrected methods (3c-methods) for their efficiency and accuracy in the geometry and relative stability of gold-thiolate nanoclusters taking Au 3(SCH3)3 isomers. Normalized mean absolute error (NMAE) is analysed to compare the results with the reference methods DLPNO-CCSD(T) and RI-SCS-MP2. The dependence of basis set size and relativistic effects on energies are also compared. TPSS shows accuracy, whereas PBE is fast for geometry optimization. On the other hand, range separation in hybrid DFAs stands out as the proper choice for the relative energies of the clusters. LC-BLYP excels, but 3c-methods are less impressive in relative stability comparison. Counterpoise corrected thiolate interaction energy and bonding analyses delineate the higher stability of bridging sulfur coordination (RS-Au-SR; R = − methyl) than singly-bonded and capping sulfur bonds in Au3(SCH3)3 . With the selected DFAs, we have analyzed the gold-sulfur interaction in Au3(SCH3)3 , and a comparison is made with AuSCH3 . The bonding analysis has revealed a partial covalency between gold and sul- fur atoms. On going from AuSCH3 to Au3 (SCH3)3 , a substantial flow of charge from gold atoms to thiolate ligands stems from the increase in gold s-d hybridization. As the s-d mixing in Au increases, the main character of Au-S interaction shifts from covalent to ionic. Hence, a covalent-charge-transfer interaction dominates in gold-sulfur bonding and gives rise to a charge-shift bonding.