  Classical molecular dynamics (MD) simulations and quantum chemical density
functional theory (DFT) calculations have been employed in the present study to
investigate the solvation of lithium cations in pure organic carbonate solvents
(ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate
(DMC)) and their binary (EC-DMC, 1:1 molar composition) and ternary (EC-DMC-PC,
1:1:3 molar composition) mixtures. The results obtained by both methods
indicate that the formation of complexes with four solvent molecules around
Li+, exhibiting a strong local tetrahedral order, is the most favorable.
However, the molecular dynamics simulations have revealed the existence of
significant structural heterogeneities, extending up to a length scale which is
more than five times the size of the first coordination shell radius. Due to
these significant structural fluctuations in the bulk liquid phases, the use of
larger size clusters in DFT calculations has been suggested. Contrary to the
findings of the DFT calculations on small isolated clusters, the MD simulations
have predicted a preference of Li+ to interact with DMC molecules within its
first solvation shell and not with the highly polar EC and PC ones, in the
binary and ternary mixtures. This behavior has been attributed to the local
tetrahedral packing of the solvent molecules in the first solvation shell of
Li+, which causes a cancellation of the individual molecular dipole vectors,
and this effect seems to be more important in the cases where molecules of the
same type are present. Due to these cancellation effects, the total dipole in
the first solvation shell of Li+ increases when the local mole fraction of DMC
is high.
