Modeling Hyperfine Coupling in Molecular Magnets

Nuclear or electron spins of magnetic molecules are promising qubit candidates¹. Electron spins are advantageous due to faster operational times, but they decohere faster due to stronger coupling to environment. This project investigates hyperfine couplings in four vanadyl complexes with long decoherence times as qubits² by electron structure calculations. In all complexes, electron spins are localized on V⁴⁺ ion. Using the analytic derivative method based on density functional theory, the Fermi-contact and spin-dipole interactions were calculated. Total hyperfine coupling to vanadium nuclear spin is compared to experiment; Using hybrid functional, good agreement can be achieved. Due to the localized nature of electron spins, the Fermi-contact interaction between an electron spin and hydrogen nuclear spin is only strong for the smallest complex. Hyperfine coupling to hydrogen nuclear spins as the main source of electron spin decoherence can be modeled by spin-dipole interactions.

¹ Leuenberger, M.N. et. al. 2001. Quantum computing in molecular magnets. Nature, 410.
² Graham, M. J. et. al. Synthetic Approach To Determine the Effect of Nuclear Spin Distance on Electronic Spin Decoherence. J. of Am. Chem. Society. 2017, 139.