van der Waals interactions are critical in Car–Parrinello molecular dynamics simulations of porphyrin–fullerene dyads

Abstract

The interplay between electrostatic and van der Waals (vdW) interactions in porphyrin-C60 dyads is still under debate despite its importance in influencing the structural characteristics of such complexes considered for various applications in molecular photovoltaics. In this article, we sample the conformational space of a porphyrin-C60 dyad using Car-Parrinello molecular dynamics simulations with and without empirical vdW corrections. Long-range vdW interactions, which are poorly described by the commonly used density functional theory functionals, prove to be essential for a proper dynamics of the dyad moieties. Inclusion of vdW corrections brings porphyrin and C60 close together in an orientation that is in agreement with experimental observations. The structural differences arising from the vdW corrections are shown to be significant for several properties and potentially less important for others. Additionally, our Mulliken population analysis reveals that contrary to the common belief, porphyrin is not the primary electron donating moiety for C60 . In the considered dyad, fullerene's affinity for electrons is primarily satisfied by charge transfer from the amide group of the linker. However, we show that in the absence of another suitable bound donor, C60 can withdraw electrons from porphyrin if it is sufficiently close.

Switching Competition between Electron and Energy Transfers in Porphyrin–Fullerene Dyads

“…12 The quality of the DFT calculations might be improved by applying dispersion corrections. 54 However, this approach requires an additional computational cost, which would be a serious problem for such large systems. A computationally cheaper approach is (1) to calibrate the DFT data using spectroscopic data for locally excited porphyrin and fullerene states, P S1 −C 60 and P−C 60 S1 , which will correct the electron correlation deficiency of DFT, and (2) to correct the energy of the charge transfer formula so that long-range Coulombic interactions, which are underestimated by DFT, are accounted for.…”

“…The quality of the DFT calculations might be improved by applying dispersion corrections . However, this approach requires an additional computational cost, which would be a serious problem for such large systems.…”

libvdwxc: a library for exchange–correlation functionals in the vdW-DF family

“…Octopus, on the other hand, has been used to simulate coherent charge transfer on very large supermolecular triads with non-adiabatic dynamics [64]. Since vdW forces appear to play a role in the charge separation in organic photovoltaics [65], vdW-DF functionals in Octopus are particularly appealing. Furthermore an interface for the planewave PAW code ABINIT [32] is planned.…”