Nonempirically Tuned Long-Range Corrected Density Functional Theory Study on Local and Charge-Transfer Excitation Energies in a Pentacene/C60 Model Complex

The local and charge-transfer excitation energies in a pentacene/C-60 complex, which is prototypical of the minimal structural unit of the donor-acceptor heterojunction in pentacene/C-60 organic cells, are evaluated using the time-dependent long-range corrected density functional theory (TD-LC-BLYP) method in comparison with those estimated from the experimental data for pentacene and C-60. In the framework of the tuned range-separated hybrid (Livshits et al. J. Phys. Chem. A 2008, 112, 12789), we tune the range separating parameter (mu) of the LC-BLYP functional by imposing the many-electron self-interaction-free (ME-SIF) condition on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of pentacene and C-60. The TD-LC-BLYP method with mu = 0.20 is found to succeed in the semiquantitative description of both the local and charge-transfer excitation energies in the pentacene/C-60 complex.