Development of Quantum Chemistry-Based Force Fields for Poly(ethylene oxide) with Many-Body Polarization Interactions
ABSTRACT 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 Møller−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.
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ABSTRACT: Quantum chemistry-based force fields with many-body polarizable interactions and two-body effective polarizability parameters have been developed for the interaction of poly(ethylene oxide) (PEO) with Li+ and BF4-. The Li+/ether repulsion parameters were found to be transferable to another polyether, such as poly(methylene oxide), that is interacting with a Li+ cation. Molecular dynamics (MD) simulations have been performed for PEO (Mw = 2380)/LiBF4 for EO:Li = 15:1 at three temperatures: 363, 393, and 423 K. The Li+ environment was found to be in reasonable agreement with that measured for other lithium salts that have been doped in PEO. MD simulations employing the many-body (MB) polarizable force field predicted ion conductivity, self-diffusion coefficients, and the slowing of the PEO dynamics upon the addition of LiBF4 salt that were in good agreement with experiments. MD simulations employing the two-body (TB) force field yielded polymer and ion dynamics that were slower than those from the simulations employing the MB force field. Analysis of the Li+ cation diffusion mechanism revealed that the Li+ cations with significant motion along PEO chains have a much higher self-diffusion coefficient than do the Li+ cations that do not undergo a noticeable motion along PEO chains, which suggests that the Li+ motion along PEO makes an important contribution to the cation diffusion mechanism.The Journal of Physical Chemistry B 07/2003; 107(28):6824-6837. · 3.38 Impact Factor
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ABSTRACT: Using 1H and 13C NMR spectra, PFG NMR self-diffusion measurements, 1H and 13C NMR relaxations and 1H NOESY NMR spectra, FTIR spectra and quantum-chemical DFT and MP2 calculations, the interaction of 1,2-dimethoxyethane (DME) with water (W) was re-examined. It was confirmed that, primarily, one W molecule forms two O···H hydrogen bonds with DME in tgt conformation. At medium and higher W contents, however, larger hydrates of DME are formed, predominantly with five W molecules. The compact structure of the hydrate is warranted by O⋯H hydrogen bonds, some of them perceptibly tighter than those in the primary hydrate, and by non-classical CH3⋯O hydrogen bonds.Chemical Physics 04/2011; 382(1):104-112. · 2.03 Impact Factor