  The entanglement in many-electron states is investigated using a global
entanglement measure, viz. average site mixedness. We have examined metallic
states of noninteracting electrons, Nagaoka and Gutzwiller states of
strongly-correlated electrons, and superconducting states. Uncorrelated
metallic states at half filling seem to maximize entanglement, as these states
optimize the number of holes, the number of doubly-occupied sites. Entanglement
is calculated explicitly for Gutzwiller-projected many-electron states in one
dimension, which have less entanglement as double occupancy is inhibited in
these states. Entanglement in superconducting states, which tend to promote
double occupancy, is calculated as a function of the energy gap, and found to
be lower than the metallic state entanglement. There is a possibility of a
regime with a nonzero single-site concurrence depending on the energy gap.
