General Force-Field Parameterization 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 inter-monomer dihedral potentials and partial charges. Our findings indicate that the use of a two-step methodology of geometry optimisation and single-point energy calculations using DFT methods produces potentials which compare favourably 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 parameterization and the scope of a given parameter set for variations to a given molecule. We perform simulations of long oligomers of dioctyl-fluorene and hexyl-thiophene in explicit solvent and find peristence lengths and end-length distributions consistent with experimental values.