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Abstract
It is a long-standing goal to understand the reaction mechanisms of catalytic metalloenzymes at an entangled many-electron level, but this is hampered by the exponential complexity of quantum mechanics. Here, by exploiting the special structure of physical quantum states and using the density matrix renormalization group, we compute near-exact many-electron wavefunctions of the Mn4CaO5 cluster of photosystem II, with more than 1 × 1018 quantum degrees of freedom. This is the first treatment of photosystem II beyond the single-electron picture of density functional theory. Our calculations support recent modifications to the structure determined by X-ray crystallography. We further identify multiple low-lying energy surfaces associated with the structural distortion seen using X-ray crystallography, highlighting multistate reactivity in the chemistry of the cluster. Direct determination of Mn spin-projections from our wavefunctions suggests that current candidates that have been recently distinguished using parameterized spin models should be reassessed. Through entanglement maps, we reveal rich information contained in the wavefunctions on bonding changes in the cycle. Many-electron quantum modelling of the metal clusters in metalloenzymes is a long-standing ambition for theoreticians. Here, using the density matrix renormalization group, the many-electron wavefunctions of the Mn4CaO5 cluster of photosystem II are computed, providing new insights into the electronic structure and reactivity at the level of many-particle quantum mechanics and entanglement. Cite this article
Kurashige, Y., Chan, GL. & Yanai, T. Entangled quantum electronic wavefunctions of the Mn4CaO5 cluster in photosystem II. Nature Chem 5, 660–666 (2013). https://doi.org/10.1038/nchem.1677 