General Force-Field Parametrization Scheme for Molecular Dynamics Simulations of Conjugated Materials in Solution

We
describe a general scheme to obtain force-field parameters for
classical molecular dynamics simulations of conjugated polymers. We
identify a computationally inexpensive methodology for calculation
of accurate intermonomer dihedral potentials and partial charges.
Our findings indicate that the use of a two-step methodology of geometry
optimization and single-point energy calculations using DFT methods
produces potentials which compare favorably to high level theory calculation.
We also report the effects of varying the conjugated backbone length
and alkyl side-chain lengths on the dihedral profiles and partial
charge distributions and determine the existence of converged lengths
above which convergence is achieved in the force-field parameter sets.
We thus determine which calculations are required for accurate parametrization
and the scope of a given parameter set for variations to a given molecule.
We perform simulations of long oligomers of dioctylfluorene and hexylthiophene
in explicit solvent and find peristence lengths and end-length distributions
consistent with experimental values.