Effect of varying the TD-lc-DFTB range-separation parameter on charge and energy transfer in a model pentacene/buckminsterfullerene heterojunction

Density-functional tight binding (DFTB) has become a popular form of approximate density-functional theory (DFT) based upon minimal valence basis set and neglect all but two center integrals. We report the results our tests recent long-range correction (lc) for time-dependent (TD) lc-DFTB by carrying out TD-lc-DFTB fewest switches surface hopping (FSSH) calculations energy charge transfer times using relatively new DFTBaby program. An advantage this method is ability to run enough trajectories get meaningful ensemble averages. Our interest in present work less determining exact rates than understanding how these vary with value range-separation parameter (Rlc = 1/{\mu}) model organic solar cell heterojunction consisting van der Waals complex P/F made up single pentacene (P) molecule together buckminsterfullerene (F) molecule. The default Rlc 3.03 a0 found be much too small as neither nor observed until ~ 10 a0. Tests at geometry show that best agreement high-quality ab-initio spectra obtained limit no lc (i.e., very large Rlc.) A plot function provided which suggests 15 yields typical literature time about 100 fs. However, high 300 fs 25 closer examination process P*/F P+/F- shows initial electron accompanied partial delocalization P hole onto F then relocalizes back P, consistent polaron-like picture nuclei relax stabilize resultant redistribution charges.