Correction for dispersion and Coulombic interactions in molecular clusterswith density functional derived methods: Application to polycyclic aromatic hydrocarbon clusters

摘要

The density functional based tight binding (DFTB) is a semiempirical method derived from thedensity functional theory (DFT). It inherits therefore its problems in treating van der Waals clusters.A major error comes from dispersion forces, which are poorly described by commonly used DFTfunctionals, but which can be accounted for by an a posteriori treatment DFT-D. This correction isused for DFTB. The self-consistent charge (SCC) DFTB is built on Mulliken charges which areknown to give a poor representation of Coulombic intermolecular potential. We propose to calculatethis potential using the class IV/charge model 3 definition of atomic charges. The self-consistentcalculation of these charges is introduced in the SCC procedure and corresponding nuclear forcesare derived. Benzene dimer is then studied as a benchmark system with this corrected DFTB(c-DFTB-D) method, but also, for comparison, with the DFT-D. Both methods give similar resultsand are in agreement with references calculations (CCSD(T) and symmetry adapted perturbationtheory) calculations. As a first application, pyrene dimer is studied with the c-DFTB-D and DFT-Dmethods. For coronene clusters, only the c-DFTB-D approach is used, which finds the sandwichconfigurations to be more stable than the T-shaped ones.