Magnetic Anisotropy in Organic Polyradicals


Type of Project: Theory Project

Location: Donostia

Daniel Reta

Magnetic anisotropy arises when the response of a material depends on its orientation with respect to an applied magnetic field. In molecules, this apparently inane feature unlocks a whole new set of electronic states, whose clever manipulation allows for original and fascinating properties. Notable examples of this are single molecule magnets[1] and spin qubits,[2] proposed as alternative platforms for information storage and quantum processing, respectively.

In practice, the number and properties of these newly available states is dictated by the zero-field splitting (ZFS). Because transition metal ions present inherently large ZFSs, metal-based molecules dominate this field of research. However, ZFS can also be promoted in organic polyradicals by exploiting the so-called spin-spin contribution,[3] with the added value that carbon-based systems could, in principle, be more easily integrated in graphene-based devices for possible spintronic applications.

Following on early results obtained in the group,[4] in this project you will study a series of m-xylylene based polyradicals to show whether helical folding, as compared to linear analogues, is an effective strategy to enhance ZFS in organic magnets. In particular, you will acquire knowledge on:

• Density Functional Theory (DFT) calculations to perform molecular geometry optimisations and calculation of ZFS parameters.
• Multiconfigurational methods (MCSCF) to accurately describe the electronic structure of the compounds and cross-validate DFT-calculated ZFS parameters.
• Quantum chemistry packages such as OpenMolcas, Gaussian and/or Orca, as well as High Performing Computing (HPC) structures, where the calculations will be run.
• Coding in Python, as an effective way to treat, organise and visualise data.
The candidate is expected to have a good knowledge of computational chemistry and electronic structure theory of molecules.

[1] Goodwin et al. Molecular magnetic hysteresis at 60 kelvin in dysprosocenium. Nature, 2017, 548, 439–442.
[2] S. L. Bayliss et al. Optically addressable molecular spins for quantum information processing. Science, 2020, 370, 1309-1312 (2020).
[3] F. Neese. Importance of Direct Spin−Spin Coupling and Spin-Flip Excitations for the Zero-Field Splittings of Transition Metal Complexes:  A Case Study. J. Am. Chem. Soc. 2006, 128, 31, 10213–10222
[4] D. Reta et al. Helical Folding-Induced Stabilization of Ferromagnetic Polyradicals Based on Triarylmethyl Radical Derivatives. J. Am. Chem. Soc., 2016, 138 (16), 5271–5275.