Assessment of Charge Transfer Energies of Noncovalently Bounded Ar-TCNE Complexes Using Range-Separated Density Functionals and Double-hybrid Density Functionals.

Charge Transfer (CT) molecular complexes have recently received much attention in a broad variety of fields. The time-dependent density functional theory (TDDFT), which is essential for studying CT complexes, is a well-established tool to study the excited states of relatively large molecular systems. However, when dealing with donor-acceptor molecules with CT characteristics, TDDFT calculations based on standard functionals can severely underestimate the excitation energies. The TDDFT methodology, combined with range-separated DFT and range-separated double-hybrid DFT functionals, had previously been used by different research groups to reliably predict the excitation energies of different charge transfer molecular complexes. We follow the same path to calculate the excited state charge transfer energy of some selected molecular complexes, such as, Ar-TCNE (TCNE=tetracyanoethylene; Ar= benzene, naphthalene, anthracene, etc.). The interactions between the donor-acceptor moieties of these molecular complexes are also studied and the relationship between the interaction and the charge transfer energies are shown here.