  We have performed a comprehensive study of the singlet ground state of two
electrons on the surface of a sphere of radius $R$. We have used electronic
structure models ranging from restricted and unrestricted Hartree-Fock theory
to explicitly correlated treatments, the last of which lead to near-exact
wavefunctions and energies for any value of $R$. M{\o}ller-Plesset energy
corrections (up to fifth-order) are also considered, as well as the asymptotic
solution in the large-$R$ regime.

Other Condensed Matter