  A theoretical treatment based upon the quasi-chemical theory of solutions
predicts the most probable number of water neighbors in the inner shell of a
Li+ ion in liquid water to be four. The instability of a six water molecule
inner sphere complex relative to four-coordinated structures is confirmed by an
`ab initio' molecular dynamics calculation. A classical Monte Carlo simulation
equilibrated 26 water molecules with a rigid six-coordinated Li(H2O)6+ complex
with periodic boundary conditions in aqueous solution. With that initial
configuration for the molecular dynamics, the six-coordinated structure relaxed
into four-coordinated arrangements within 112 fs and stabilized. This
conclusion differs from prior interpretations of neutron and X-ray scattering
results on aqueous solutions.
