Performance of Density Functionals and Semiempirical 3c Methods for Small Gold-Thiolate Clusters

Amid the surge of computational studies of gold thiolate clusters in the recent past, we present a comparison of popular density functionals (DFAs) and three-part corrected methods (3c-methods) on their performance by taking a dataset consisting 18 isomers of Aun(SCH3)m (m ≤ n =1-3) stoichiometry. We have compared the efficiency and accuracy of the DFAs and 3c-methods in geometry optimization with RI-SCS-MP2 and energies with DLPNO-CCSD(T) as reference methods. The lowest energy structure out of the largest stoichiometry from our dataset i.e., Au3(SCH3)3 is considered to evaluate the computational time for SCF and gradient. Alongside, the number of optimization steps to locate the most stable minima of Au3(SCH3)3 are compared to assess the efficiency of the methods. A comparison of relevant bond lengths with the reference geometry was made to estimate the accuracy in geometry optimization. Some methods such as LC-BLYP, ⍵B97M-D3BJ, M06-2X, and PBEh-3c are unable to locate many of the minima that are found by most of the other methods; thus, the versatility in locating various minima is also an important criterion in choosing a method for the given project. We have compared the relative energies among the isomers along every stoichiometric series and the interaction energy of the gold core with the ligands to estimate the accuracy of the methods. The dependence of basis set size and relativistic effects on energies are also compared. Some of the highlights are the following. TPSS shows accuracy, whereas mPWPW is fast with comparable accuracy. The range separated hybrid DFAs are the best choice for the relative energies of the clusters. CAM-B3LYP excels, whereas B3LYP shows poor performance. Overall, LC-BLYP is a balanced performer considering both the geometry and relative stability of the structures, but it lacks diversity. The 3c-methods, although fast, are less impressive in relative stability.