Development of Quantum Chemistry-Based Force Fields for Poly(ethylene oxide) with Many-Body Polarization Interactions
A methodology for consistent development of the quantum chemistry-based force fields with and without many-body polarizable terms is described. Adequate levels of theory and basis sets for determination of the relative conformational energetics, repulsion and dispersion nonbonded parameters, dipole moments, and molecular polarizability are established. Good agreement between the quantum chemistry-based repulsion and dispersion parameters and those previously obtained by fitting crystal structures of poly(oxymethylene) is obtained. Hartree?Fock (HF) calculations with augmented correlation consistent basis sets are adequate for the determination of repulsion parameters, whereas a double extrapolation to improved treatments of electron correlations and larger basis sets is needed to obtain dispersion parameters. Partial charges are obtained by fitting to the electrostatic grid of model compounds. Atomic polarizabilities are fitted to reproduce polarization energy around the model compounds. The density functional B3LYP yields relative conformational energies in better agreement with M?ller?Plesset second-order (MP2) perturbation theory than the HF energies; however, the accuracy of the B3LYP density functional was insufficient to provide reliable relative conformational energetics. A molecular mechanics study of the conformational energetics of 1,2-dimethoxyethane indicated that many-body polarizable interactions have little impact on the relative conformational energies.