All-Atom Reactive Monte Carlo Molecular Dynamics for Molecular Doping in Organic Semiconductors

The computational study of molecular doping in organic semiconductors (OSCs) is challenged by multiple competing length and time scales. We present an all-atom Reactive Monte Carlo Molecular Dynamics (RMCMD) method for quantitatively determining molecular doping efficiency in OSCs. A Metropolis criterion is employed for the doping reaction, which is parametrized from density functional theory (DFT) calculations of energetics and atomic partial charges of the doped and neutral molecular species. Polaronic effects are included in the RMCMD method to enable geometric reorganization upon doping, including the flattening of the inter-ring dihedrals. Extensions to partial charge transfer states are also developed to allow for the inclusion of charge transfer complexes. To demonstrate the validity of the approach, the doping efficiency and radial distribution function of a poly(3-hexylthiophene) system doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane are calculated in an amorphous morphology. The method is implemented as a fix in LAMMPS, with the code made publicly available on GitHub.