Speaker:Professor Mark Pederson

Professor Mark Pederson

University of Texas - El Paso

Title: Molecular magnets for quantum sensing of chemical reactions and qubits

Abstract: In this talk, the computational and theoretical challenges associated with the accurate quantum-mechanical computational description of molecular magnets [1] and recent quantum simulations [2-4] are presented within the context of recent experiments [5-7]. One example demonstrates that resonant tunneling of magnetization can deduce the chemical splitting of water into hydroxyl and hydrogen molecules. The second example demonstrates how computational density-functional-based methods are used to accurately determine the properties and complexities of putative molecular magnetic qubits that are composed of a perfect triangle of half-integer spin metal ions [3,4] and to suggest additional experiments. The Mn₁₂O₁₂(COOR)₁₆(HOH)₄ molecule, with S₄ symmetry, has four of everything. Our recent calculations find that this system readily accepts four excess electrons at the cost of only 0.32 eV in vacuum. It exhibits a macro-spin with S=10 and received significant past interest due to its of quantum tunneling of magnetization (QTM). We show that the spectroscopic signatures associate with QTM are sensitive to the presence of the four HOH terminators (e.g. 4 waters vs. 2H₂ and 2OH) and to the number of added electrons (0 vs. 4). As such, QTM can provide an ultra-low-energy non-destructive technique for observation of water decomposition in a molecule that bears a striking similarity to the reaction center in the oxygen-evolving complex [2,7]. Recently, Boudalis et al have experimentally observed the magneto-electric effect in a chiral Fe₃O(NC₅H₅)₃(O₂CC₆H₅)₆ molecule [5] and have noted further that this is the first possible spin-electric system based upon spin 5/2 metal centers. Our results [3], using standard density-functional methods, show that the spin-electric behavior of this molecule could be even more interesting as there are energetically competitive reference states with high and low local spins (S=5/2 vs. S=1/2) on the Fe³⁺ ions. We provide predictions of magnetic and x-ray spectroscopies to deduce the presence of both states. Possible uses for low-temperature quantum sensing of fields and pressure variations are suggested. Recent efforts at improving quantum approximations for such systems will be highlighted [1] and at designing chemical qubits will be reviewed.

Bio: Dr. Pederson's research is in chemical physics, condensed-matter physics, and computational physics. He has continuously concentrated on next-generation computing paradigms for quantum mechanics. Dr. Pederson’s pioneering work demonstrated the quantitative computational prediction of quantum tunneling of magnetization (QTM) and spin-electric effects in molecular magnets. Both of these different collective phenomena arise from the spin of the electron. Quantitatively understanding conditions that allows for such coherent phenomena, is necessary from the standpoint of spin-Qubit design in quantum information science and may also unlock the mysteries of bio-navigation. He is currently attempting to link the fields of molecular magnetism and photocatalytic water splitting by demonstrating that variations in QTM, in reacting systems, can be used to spectroscopically sense conversion of water into oxygen and hydrogen without pumping energy into the system. Dr. Pederson is the primary author of a computer code, the Naval Research Laboratory Molecular Orbital Library (NRLMOL), that describes how nanoscale systems interact with electromagnetic radiation. The opportunity to concentrate on developing this code over a long period has enabled these unique computational investigations and predictions. 

^{[1] M.R. Pederson, A Ruzsinszky and J. P. Perdew, Communication: Self-Interaction Correction with Unitary Invariance in Density Functional Theory, J. of Chem. Phys., 140, 121103 (2014).}

^{[2] J. Batool, T. Hahn and M.R. Pederson, Magnetic Signatures of Hydroxyl and Water Terminated Neutral and Tetra-anionic Mn₁₂-Acetate, J. Comput. Chem. 25, 2301-2308 (2019).}

^{[3] M. F. Islam, J. F. Nossa, C. M. Canali and M. Pederson, First-principles study of spin-electric coupling in a Cu₃ single molecular magnet, Phys. Rev. B 82 155446 (2010).}

^{[4] A. I. Johnson, M. F. Islam, C. M. Canali and M. R. Pederson, A Multiferroic molecular magnetic qubit, Submitted to J. Chem. Phys. 151, 174105 (2019).}

^{[5] B. Georgeot & F. Mila, Chirality of triangular antiferromagnetic clusters as a qubit, PRL 104, 200502 (2010).}

^{[6] A. K. Boudalis, J. Robert & P. Turek, 1st demonstration of magnetoelectric coupling in a polynuclear molecular nanomagnet via EPR studies Fe₃O(O₂CPh)₆(Py)₃ClO₄, Chem. Eur. J 24 14896-14900 (2018).}

^{[7] G. Maayan, N. Gluz, G. Christou, A bioinspired soluble manganese cluster as a water oxidation electrocatalyst with low overpotential, Nat. Catal. 48 1 (2018).}