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Density‐functional calculations of spin coupling in [Fe 4 S 4 ] 3+ clusters
Author(s) -
Mouesca JeanMarie,
Noodleman Louis,
Case David A.
Publication year - 1995
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560560710
Subject(s) - hamiltonian (control theory) , delocalized electron , density functional theory , chemistry , coupling constant , condensed matter physics , cluster (spacecraft) , valence (chemistry) , antiferromagnetism , molecular physics , physics , computational chemistry , quantum mechanics , mathematical optimization , mathematics , computer science , programming language , organic chemistry
We present nonlocal density‐functional calculations for a model of the [Fe 4 S 4 ] 3+ cluster found in high potential iron proteins, which consists formally of a ferric pair Fe 3+ Fe 3+ and a mixed‐valence pair Fe 2.5+ Fe 2.5+ . Three Spin Hamiltonian parameters, J (the interlayer Heisenberg interaction), B (a resonance delocalization term) and Δ J 12 (associated with the ferric pair) have been estimated using density‐functional energies of a high‐spin state as well as two different broken symmetry states. We obtain J =673 cm −1 , B =878 cm −1 , and Δ J 12 =160 cm −1 . These results are discussed in the light of experimental work on a model compound in the same oxidation state, in which the temperature dependence of the magnetic susceptibility was analyzed with this sort of spin Hamiltonian. Good overall agreement between theory and experiment ( J =652 cm −1 , B =592 cm −1 ), and Δ J 12 =145 cm −1 is found. In particular, the antiferromagnetic spin coupling constant for the ferric pair exceeds in magnitude all other Heisenberg‐type interactions (Δ J 12 > 0) as expected from previous theoretical and experimental work; this is the first time that the broken symmetry method has been used to analyze a spin Hamiltonian with multiple coupling constants in an Fe 4 S 4 cluster. © 1995 John Wiley & Sons, Inc.