Alkaline-earth triplet spectrum — outer valence electron with inner-s Hartree screening
Model an alkaline-earth atom as 2+2 (or 0+2 for He): closed-shell inner core absorbed
into a reduced kernel of charge Zkernel, plus two valence electrons. In the excited
triplet state, one valence electron stays in the ground s orbital (creating a Hartree screening
parameterized by Zinner) and the other is the explicit "outer" electron. The outer
electron solves
−½u″ + [ℓ(ℓ+1)/(2r²) + V_eff(r)]u = Eu
on r ∈ [r_c, R_max] with empty-core + Neumann at r_c, where
V_eff(r) = −Zkernel/r + V_H(r; Zinner),
V_H(r) = (1/r)·[1 − (1+Zinner·r)·exp(−2Zinner·r)]
He: r_c=0, Zkernel=2, Zinner≈1.69 (Slater for 1s). Be: r_c absorbs [He],
Zkernel=2, Zinner≈2.3 (Slater for 2s). Same shape for Mg, Ca.
Model vs observed (Ha)
RMS error — Ha over fitted levels.