Modeling silver clusters-hydrocarbon interactions: A challenge for SCC-DFTB

Abstract

This work examines the reliability of the Self Consistent Charge Density Functional based Tight Binding (SCC-DFTB) scheme to derive geometrical and thermochemistry observables for complexes and clusters made of Ag, C and H atoms. In addition to the currently available DFTB parameterization DFTBhyb, it proposes a new SCC-DFTB parameterization based on DFT Slater Koster integrals and recalibrated on atomic pairs MRCI calculations for clusters made of Ag, C and H atoms. Two sets of parameters were determined, one for restricted open-shell SCC-DFTB, the other for spin-polarized SCC-DFTB. These two new sets of parameters, namely DFTBγand DFTBγpol respectively, along with DFTBhyb, are first tested on Agn, AgnC and AgnH clusters. A key issue being the transferability of such parameters on different types of Ag-X bonds, the three sets of parameters are then tested on AgmCnHp (m = 1-3, n = 2, p = 0-2) complexes involving covalent and π metal-ligand bonds. The particular case of naphthalene C10H8 as a π-ligand is also investigated. In general, with respect to DFTBhybresults, using DFTBγparameters leads to an improvement of geometries and energetics. In the case of AgnC10H8 clusters, the role of dispersion is evidenced. However, in a few cases, the geometries may distort due to a questionable description of charge transfer with DFTBγand DFTBγpol . The spin-polarized version of SCC-DFTB is suited to correctly describe open-shell species with more than one unpaired electron in their ground electronic state but is shown not to improve the results otherwise.