(663b) Development of an Opls-Aa Style Forcefield for Polythiophenes

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 and this presentation focus on the optimization of thiophene parameters and development of bithiophene parameters for use in the framework of the 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* level. 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 comparison was made between the quantum mechanical potential surface versus the classical energy surface that results from the old and new forcefield parameters.