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

Ab initio and molecular mechanics studies of LiPF 6 and the interaction of the salt with the poly(ethylene oxide) (PEO) oligomer dimethylether have been performed. Optimized geometries and energies of Li + /PF 6 − 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 + /PF 6 − complex. By contrast, analogous studies of PF 6 − /PF 6 − and PF 6 − /dimethyl ether complexes revealed important contributions of electron correlation to the complex interaction energy. A molecular mechanics force field for simulations of PEO/LiPF 6 melts was parameterized to reproduce the geometries and energies of Li + /PF 6 − , PF 6 − /PF 6 − , PF 6 − /dimethylether complexes. Molecular dynamics simulations of PEO/LiPF 6 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/LiPF 6 solutions was found to be within an order of magnitude of the experimental values.