  The stationary nonempirical simulations of Na+(H2O)n clusters with n in a
range of 28 to 51 carried out at the density functional level with a hybrid
B3LYP functional and the Born-Oppenheimer molecular dynamics modeling of the
size selected clusters reveal the interrelated structural and energetic
peculiarities of sodium hydration structures. Surface, bulk, and transient
configurations of the clusters are distinguished with the different location of
the sodium nucleus (close to either the spatial center of the structure or one
of its side faces) and its consistently changing coordination number (which
typically equals five or six). The <rNaO> mean Na-O distances for the
first-shell water molecules are found to depend both on the spatial character
of the structure and the local coordination of sodium. The <rNaO> values are
compared to different experimental estimates, and the virtual discrepancy of
the latter is explained based on the results of the cluster simulations.
Different coordination neighborhoods of sodium are predicted depending on its
local fraction in the actual specimens.
