Study of adiabatic connection in density functional theory with an accurate wavefunction for 2-electron atoms

Using an accurate semi-analytic wavefunction for two electron atoms, we construct the external potential for varying strength of electron-electron (e-e) interaction. Using this potential we explicitly calculate the energy of their positive ion and show that the ionization-potential of these systems remains unchanged with respect to the strength parameter for e-e interaction. Furthermore, using total energies of these systems as a function of strength parameter, we provide a new perspective into a variety of hybrid functionals.