title: Entangled quantum electronic wavefunctions of the Mn₄CaO₅ cluster in photosystem II.
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 × 10(18) 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.
authors.affiliation: Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Aichi 444-8585, Japan. kura@ims.ac.jp
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kurashige
authors.forename: Garnet Kin-Lic
authors.initials: GK
authors.lastname: Chan
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yanai
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D010087:Oxides / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D017610:Calcium Compounds; D010087:Oxides; D045332:Photosystem II Protein Complex; D008345:Manganese; C016538:lime