(159d) Polythiophene Forcefield Parameterization

Quantum-mechanics calculations and molecular simulations have been conducted for a series of thiophene and alkyl-substituted thiophene oligomers. The long-term goal of this research is to examine, through molecular modeling, the impact of multiple chain (or ?aggregation?) effects on thermochromic properties of poly(3-alkylthiophenes). Initial investigations have focused on optimization of thiophene parameters and development of bithiophene parameters for us in OPLS-aa forcefield. All intra ring potential surfaces and inter-ring angle-bending and bond stretching were developed from quantum mechanical calculations at the HF/6-31G*//MP2/6-31G*. The inter-ring torsions were developed from a HF/6-31G*//MP2/6-31G+* calculation. New and optimized parameters were derived using a least-squares minimization and a comparision was made between old and new parameters versus the quantum mechanical potential surface through a monte carlo simulation.