UPPER-BOUNDS TO THE ELECTRON-ELECTRON COALESCENCE DENSITY IN TERMS OF THE ONE-ELECTRON DENSITY-FUNCTION

An expression that allows one to evaluate the electron-electron coalescence density in terms of the one-electron density function at the Hartree-Fock level is derived. Then it is shown, by calculation with highly accurate wave functions of He-like ions, that this expression represents a simple and accurate upper bound to the electron-electron coalescence density for nearly exact wave functions.