We prove that, in the large-dimension limit, the high-density correlation
energy \Ec of two opposite-spin electrons confined in a D-dimensional space
and interacting {\em via} a Coulomb potential is given by \Ec \sim -1/(8D^2)
for any radial confining potential V(r). This result explains the observed
similarity of \Ec in a variety of two-electron systems in three-dimensional
space.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let