 Slater's rules

An empirical orbital-screening prescription. Other electrons in an $ns,np$ group count $0.35$ each; electrons in shell $n-1$ count $0.85$, deeper electrons $1.00$, and outer electrons zero. For $1s$, the partner contributes $0.30$. d and f groups use separate rules.^[ref]

Slater's rules are a set of guidelines used in quantum chemistry and atomic physics to approximate the effective nuclear charge (\(Z_{\text{eff}}\)) experienced by an electron in a multi-electron atom. Developed by John C. Slater, these rules provide a way to account for the shielding effect that occurs due to the presence of other electrons in the atom.