title = {Ground state of two electrons on a sphere},
volume = {79},
abstract = {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 theories to explicitly correlated treatments, the last of which leads to near-exact wave functions and energies for any value of R. Møller-Plesset energy corrections (up to fifth-order) are also considered, as well as the asymptotic solution in the large-R regime.},
pages = {062517},
number = {6},
journaltitle = {Physical Review A},
shortjournal = {Phys. Rev. A},
author = {Loos, Pierre-François and Gill, Peter M. W.},
abstract = {Meller-Plesset perturbation calculations ({MPn}) up to fiftieth order, within both the restricted ({RHF}) and unrestricted Hartree-Fock ({UHF}) frameworks, have been used to examine the He2+2 ground-state potential curve. The bond lengths of the equilibrium and transition structures have been optimized at all orders of perturbation theory. It is found that {RMP} n describes the homolytic dissociation better than {UMPn} for all n {\textgreater} 2. This unexpected behaviour may be attributed to spin contamination in the {UHF} wavefunction. The {UMPn} barriers deceptively appear convergent for small n and the results may be indicative of dangers inherent generally in using the {UMP} approach with significantly spin-contaminated wavefunctions.},