FIG. 1: 15 -27 -24 -21 -18 -15 -12 -9 -6 -3 0 -10 0 10 -10 0 10 -10 0 10 O$_{2}$/Al(111) O$_{2}$/Mg(0001) O$_{2}$/Pb(111) Energy (eV) $^{π}$p * $^{π}$p $^{σ}$p $^{σ}$s * (b) (c) (a) s p DOS (arb.units) $^{σ}$s