Cedric Weber, David D. O'Regan, Nicholas D. M. Hine, Peter B. Littlewood, Gabriel Kotliar, Mike C. Payne
We propose a mechanism for binding of diatomic ligands to heme based on a dynamical orbital selection process. This scenario may be described as bonding determined by local valence fluctuations. We support this model using linear-scaling first-principles calculations, in combination with dynamical mean-field theory, applied to heme, the kernel of the haemoglobin metalloprotein central to human respiration. We find that the subtle variations in Hund's exchange coupling induce an iron 3d orbital selection process, by which out-of-plane orbital hybridization is enhanced at the expense of an increase of valence fluctuations, characterized by the von Neumann entropy. We obtain excellent agreement between our computed optical absorption spectra and experimental data, our picture accounting for the observation of optical transitions in the infrared regime. Based on out-of-equilibrium calculations, we propose a new, sensitive method for the profiling of heme binding by means of strong ligand-dependence of the dynamical magnetic response.
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http://arxiv.org/abs/1206.0412
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