“…6 confirms the presence of two irreducible submatrices of H Fz =0 . Indeed, the two uncoupled subspaces are spanned by the states |Ψ i with i = 1, 2, 5, 7,8,11,15,16,18,21,22, 24 (subspace I), and |Ψ j with j = 3, 4,6,9,10,12,13,14,17,19,20,23 (subspace II). An ordering of the eigenvalues reveals that one can have coupling among the S-S and P -P states (distributed among atoms A and B), forming submanifold I, and among all S-P and P -S states (distributed among atoms A and B), forming submanifold II.…”