Non-Hund state

Note that the superscript indicates the Af -value of the function. In addition we also define a local singlet with the same orbital occupancy but a different spin coupling. This CSF dominates the lowest excited singlet state in octahedral Ni + complexes and will be named here a non-Hund state... 

These six CSFs can be combined to form spin eigenstates three states with local triplet coupling on both magnetic centers and three more with at least one magnetic center in a locally excited (non-Hund) state. 

The simultaneous interaction of the ionic CSFs with S/ T and NH3/NH2 makes that the non-Hund states gain some weight in the wave function of the lowest triplet and singlet states. This is exactly the same mechanism as in the configuration interaction of singles and doubles. The singles have no direct interaction with the Hartree-Fock determinant due the Brillouin theorem, but they appear in the Cl wave function due to an indirect interaction via the doubles. 

Rationalize the relative size for the estimates of J extracted from the singlet-triplet and from the triplet-quintet energy difference. Hint compare the matrix elements of the ionic determinants with the non-Hund states and take into consideration the relative energy of the non-Hund states involved in... 

It remains to establish which state, singlet or triplet, is most strongly affected by the interaction with the non-Hund states. For this purpose, we have decomposed the DDCI wave functions of the different spin states and listed the coefiticients of... 

The total wave functions of the binuclear complex can be constructed from the products of these local functions. In order to find any possible interactions between the lowest singlet, triplet and quintet states and the newly introduced non-Hund... 

In the simplest description of the hopping, the on-site exchange integral is assumed to be so large in comparison to the other parameters that the doublet states dominated by the non-Hund determinants are not relevant and the energy of the lower doublet states can be simplified to... 

Scheme 3 Example applications of spin parity to alternant non-Kekule hydrocarbons. All of these are predicted triplet ground states by Hund s law-based models such as that of Longuet-Higgins.65.

Through studies exemplified by those described above, Hund s rule as a prime directive predicting HS ground states in all non-Kekule molecules was eventually ruled out. The Ovchinnikov-Klein and Borden-Davidson approaches are now frequently used to predict ground spin states for... 

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