Correlated wavefunctions for two-electron systems using new screened hydrogen-like orbitals

A simple correlated wavefunction (with explicit dependence upon the interelectronic distance r 12 ) is presented. The use of new screened hydrogen-like orbitals allows the determination of an analytic wavefunction having an exact behaviour when the two electrons are close to the nucleus, or when an electron moves at large distances from the other one. A scale parameter q e has been introduced in the Coulombic term q e /r 12 . In a variational approach, the authors have calculated average values for helium-like systems, showing an overall accuracy about 0.1% on the energies, with a three-parameter monoconfigurational wavefunction.