(a) Deviations between the calculated ?HOMO and -Ive and between Ive and Iexp for a series of HeM clusters. In each cluster all the He atoms are chemically equivalent. The nearest neighboring atoms are separated by 10Å, and the Iexp of HeM is well approximated by Iexp of a He atom. (b) Calculated total energy deviation from the linearity condition of a fractionally charged He atom as a function of the fractional charge δ. Here ΔE(Heδ+) = E(Heδ+)-δE(He+)-(1-δ)E(He), and the δ values have been scaled in the figure for a direct comparison with (a).