We discuss an approach to accurate numerical computations of slowly convergent properties in two-electron atoms/ions which include the negatively charged Ps$^{ -}$ ($e^{ -} e^{ +} e^{ -}$) and H$^{ -}$ ions, He atom and positively charged, helium-like ions from Li$^{ +}$ to Ni$^{ 26+}$. All these ions are considered in their ground $1^{ 1}S-$state(s). The slowly convergent properties selected in this study include the electron-nulceus $\langle r^{ 2 k}_{ eN} \rangle$ and electron-electron $\langle r^{ 2 k}_{ ee} \rangle$ expectation values for $k$ = 2, 3, 4 and 5.
Categories: physics.atom-ph astro-ph.SR