Magneto-Electric Coupling, Chirality, and Symmetry Considerations in Molecular Spin Systems

Speaker: Mark Pederson
Affiliation: University Texas At El Paso
Date: October 31^st

Abstract: 

In the first half of the talk I will provide a basic tutorial on how to perform density-functional calculations on molecular materials and discuss a solution to a problem known as the self-interaction error to density functional theory. Then I will discuss it within the context of broken symmetry molecules and the strategy they use to potentially restore their symmetry – e.g. chirality. Three spin systems with molecular backbones that exhibit, at least primarily, three-fold rotation axes, but have additional structure or symmetry breakings that prevent the systems from fitting into the simplest possible picture of a chiral spin-electric qubit. These systems include the chiral Fe3O(NC5H5)3(O2CC6H5)6 molecular cation, which does indeed have a perfect C3 symmetry, the K6V15As6O42 neutral system with symmetry that, in principle, is higher than C3 symmetry, and the (C5H5N)Co+2{[m-PO2CH2(C6H5)2]-}3Co+2(C5H5N)3(ClO4){-1} which, as a single moiety, cannot have three-fold symmetry due to the symmetry breaking of the pyridine ligand and perchlorate ion (Fe3, V15 and Co2 respectively). With proper spin alignments, each of these systems can exhibit three-fold symmetry. However, in addition to pyridine-induced non-idealities in the Co2 system, the V15 and Fe3 exhibit their own non-idealities. The Ms=1/2 configurations that contribute primarily to the lowest-energy Kramers doublets in V15 and Fe3 moieties have a choice between equilateral-to-isosceles distortion of the triangles (high-field dipole-carrying state) and acceptance of equilateral triangles with chiral eigenstates which then provides the possibility of optically induced manipulations. This is further complicated by the presence of the molecules of crystallization/encapsulation (V15) and the presence of high-to-low spin couplings in Fe3. I will discuss the possibility of restoring the chirality and symmetry of the moieties, in their non-ideal states, through appropriate assembly on a lattice and attempt to show how consideration of vibrational and electronic excitations can couple to and possibly enable control of the resulting qubit assemblies. Calculations have been possible for decades but complexities for full-scale understanding require the data-enabled machine-learning tools that are now able to address the myriad possibilities. Calculations using model Hamiltonians, developed with DFT and FLOSIC-DFT methods, will be discussed in conjunction with our plans to use these molecules as learning tools on novel computer platforms hosted by PNNL and Microsoft. MRP, TB, EB, KK, YY, KAJ, MFI, and KW were supported by the PNNL Tec4 initiative.