Small Gold-Thiolate Clusters Au3(SMe)3: Benchmarking of Density Functionals and Bonding Analysis

We present a benchmark study on popular density functionals for their efficiency and accuracy in the geometry and relative stability of gold-thiolate nanoclusters taking Au3(SMe)3 isomers. We have used normalized mean absolute error (NMAE) analysis as a parameter to compare the results with the reference methods - DLPNO-CCSD(T) and RI-SCS-MP2. We have also compared the performance on the thiolate interaction energy of the stable geometries using the results from our benchmark study. One of the promising functional is PBE that shows robust performance for geometry optimization. On the other hand, M06-2X stands out as the proper choice for the relative energies of the clusters. With the selected methods, we have analyzed the gold-sulfur interaction in Au3(SMe)3 and a comparison is made with AuSMe. The bonding analysis has revealed a partial covalency between gold and sulfur atoms in general. On going from AuSMe to Au3(SMe)3, a substantial flow of charge from gold atoms to thiolate ligands as a result of 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.

Accurate predictions of the electronic excited states of BODIPY based dye sensitizers using spin-component-scaled double-hybrid functionals: a TD-DFT benchmark study

The excitation energies of 13 BODIPY dye sensitizers are benchmarked by means of TD-DFT, using 36 functionals. Spin-component-scaled double-hybrid (DSD) functionals are found to show the best performance.

Evaluating Fast Methods for Static Polarizabilities on Extended Conjugated Oligomers

Given the importance of accurate polarizability calculations to many chemical applications, coupled with the need for efficiency when calculating the properties of sets of molecules or large oligomers, we present a benchmark study examining possible calculation methods for polarizable materials. We first investigate the accuracy of highly-efficient semi-empirical tight-binding method GFN2-xTB, and the popular D4 dispersion model, comparing its predicted additive polarizabilities to ωB97X-D results for a subset of PubChemQC and a compiled benchmark set of molecules spanning polarizabilities from approximately 3-600 Å^3, with a few compounds in the range of approximately 1200-1400 Å^3. Although we find GFN2 to have large errors with polarizability calculations, on large oligomers it would appear a quadratic correction factor can remedy this. We also compare the accuracy of DFT polarizability calculations run using basis sets of varying size and level of augmentation, determining that a non-augmented basis set may be used for highly polarizable species in conjunction with a linear correction factor to achieve accuracy extremely close to that of aug-cc-pVTZ.