K-bar_dd coefficients: {2: '2/35', 4: '4/63'}
K-bar_ff coefficients: {2: '8/225', 4: '8/297', 6: '200/5577'}

Condon-Shortley d5 6S check:
  k=2: -35 * F_2   [expected -35]
  k=4: -315 * F_4   [expected -315]

Indicative: K-bar_ff(4f) = 0.583 eV, K-bar_dd(5d) = 0.738 eV
            rho = K_dd/K_ff = 1.265
Sanity: 6*K_ff = 3.50 eV
