  Atomic $4f$ states have been found to be essential players in the physical
behavior of lanthanide compounds, at the Fermi level $E_F$ as in the proposed
topological Kondo insulator SmB$_6$, or further away as in the magnetic
superconductor system ${\cal R}$Ni$_2$B$_2$C (${\cal R}$=rare earth ion) and in
Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$, where the $4f$ shell of Pr has a devastating
effect on superconductivity. In hole-doped ${\cal R}$NiO$_2$, the ${\cal R}$=Nd
member is found to be superconducting while ${\cal R}$=La is not, in spite of
the calculated electronic structures being nearly identical. We report first
principles results that indicate that the Nd $4f$ moment affects states at
$E_F$ in infinite-layer NdNiO$_2$, an effect that will not occur for LaNiO$_2$.
Treating 20% hole-doping in the virtual crystal approach indicates that 0.15
holes empty the $\Gamma$-centered Nd-derived electron pocket while leaving the
other electron pocket unchanged; hence Ni only absorbs 0.05 holes; the La
counterpart would behave similarly. However, coupling of $4f$ states to the
electron pockets at $E_F$ arises through the Nd intra-atomic $4f-5d$ exchange
coupling $K\approx 0.5$ eV and is ferromagnetic (FM), i.e. anti-Kondo, in sign.
This interaction causes spin-disorder broadening of the electron pockets and
should be included in models of the normal and superconducting states of
Nd$_{0.8}$Sr$_{0.2}$NiO$_2$ The Ni moments differ by 0.2$\mu_B$ for FM and
antiferromagnetic alignment (the latter are larger), reflecting some itineracy
and indicating that Heisenberg coupling of the moments may not provide a
quantitative modeling of Ni-Ni exchange coupling.
