title: Comparison of Semiempirical ZILSH and DFT Calculations of Exchange Constants in the Single Molecule Magnet [Fe8O2(OH)12(tacn)6](8.).
abstract: The exchange constants describing magnetic interactions between high spin Fe(3+) ions in the complex [Fe8O2(OH)12(tacn)6](8+) have been estimated with the semiempirical ZILSH method, and the results compared to those of DFT calculations and experimental magnetic studies. The ZILSH method provides more accurate estimates of the exchange constants than the DFT calculations, particularly for the "body-body" interaction within the central Fe4 "butterfly" unit of the complex. This interaction is found to be antiferromagnetic, which contrasts with the DFT description but is in agreement with experimental studies on smaller Fe4 butterfly complexes and known empirical correlations between exchange constants and structural parameters. The ground-state wavefunction obtained by diagonalizing the Heisenberg spin Hamiltonian matrix has a spin of ten, in agreement with previous experimental and theoretical studies. Spin alignments in the ground state demonstrate how spin frustration can lead to nonzero spin in complexes with exclusively antiferromagnetic exchange interactions.
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University [Formula: see text] Purdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202.
authors.forename: Ted A
authors.initials: TA
authors.lastname: O'Brien
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University [Formula: see text] Purdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: O'Callaghan