Entanglement entropies in the ground states of helium-like atoms
  We examine the entanglement in the ground states of helium and helium-like ions using an original Hylleraas expansion. The von Neumann and linear entropies of the reduced density matrix are accurately computed by performing the Schmidt decomposition of the S singlet spatial wavefunctions. The results presented are more accurate than currently available in published literature. 
Przemyslaw Koscik, Anna Okopinska
quant-ph cond-mat.str-el physics.atom-ph