Adsorption of Organic Electron Acceptors on Graphene-like Molecules: Quantum Chemical and Molecular Mechanical Study
Abstract
Various cluster models of graphene and a periodic graphene with two organic electron acceptors (tetracyanoethylene and tetracyanoquinodimethane) were investigated by means of several quantum chemical and molecular mechanical approaches. The benchmark interaction energies of the coronene complexes were calculated at the MP2.5/CBS/6-31G*(0.25) level of theory.
The SCS-MI-MP2, BLYP-D3 and, surprisingly, also AMBER showed modest agreement in the absolute as well as relative interaction energies. Consequently, larger complexes were investigated at these lower levels of theory including also DFTB-D.
Charge transfer was calculated on the basis of Mulliken and NBO analysis. A high correlation between the interaction energies and charge transfer was observed.
Further, vibrational analysis of the complexes revealed the association free energies for the gas phase and aqueous environment at the DFTB-D and AMBER levels. Extensive potential of mean force molecular dynamics simulations were carried out for all of the graphene organic acceptor complexes.
The convergence with the graphene model size was observed for the interaction energies as well as for the association free energies, which justifies using a cluster graphene model when the periodic one is not accessible. The role of translational entropy loss upon binding and the solvent contribution were discussed thoroughly.