Ab initio quantum chemistry and molecular dynamics simulations studies of LiPF6/poly(ethylene oxide) interactions

Ab initio and molecular mechanics studies of LiPF₆ and the interaction of the salt with the poly(ethylene oxide) (PEO) oligomer dimethylether have been performed. Optimized geometries and energies of Li⁺/PF₆^? complexes obtained from quantum chemistry revealed a preference for C_3V symmetry structures for Li⁺–P separations under 2.8 Å, C_2V symmetry for Li⁺–P in the range of 2.8–3.3 Å and C_4V symmetry for Li⁺–P separations larger than 3.3 Å. Electron correlation effects were found to make an insignificant contribution to binding in the Li⁺/PF₆^? complex. By contrast, analogous studies of PF₆^?/PF₆^? and PF₆^?/dimethyl ether complexes revealed important contributions of electron correlation to the complex interaction energy. A molecular mechanics force field for simulations of PEO/LiPF₆ melts was parameterized to reproduce the geometries and energies of Li⁺/PF₆^?, PF₆^?/PF₆^?, PF₆^?/dimethylether complexes. Molecular dynamics simulations of PEO/LiPF₆ melts were performed to validate this quantum chemistry‐based force field. Accurate reproduction of the increase in solution density with addition of salt was found while the electrical conductivity of PEO/LiPF₆ solutions was found to be within an order of magnitude of the experimental values. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 641–654, 2001