Is the effective nuclear charge only defined for valence electrons? I've just been taught about the effective nuclear charge and screening effect in school. I'd like to ask and confirm if the effective nuclear charge is only defined for valence electrons. If not then why don't we consider the repulsion from the electrons further away from the nucleus than the test electron, which by common sense should add to the attractive force by nucleus?
$Z=Z_{eff}+\sigma$, where $\sigma$ is shielding constant calculated according to Slater's rule. Since Slater's rule can be applied to any electron regardless of whether or not it's a valence electron, I think $Z_{eff}$ and $Z$ can be defined for any electron too, $Z$ in particular remaining constant.
The effect of outer electrons not being taken is also explained by Slater's rules empirically.