Year: 2023
Type: article
Abstract: We investigate hyperfine interaction (HFI) using density-functional theory for several open-shell planar $s{p}^{2}$-carbon nanostructures displaying $\ensuremath{\pi}$ magnetism. Our prototype structures include both benzenoid ($[n]\mathrm{triangulenes}$ and a graphene nanoribbon) as well as nonbenzenoid (indene, fluorene, and indene[2,1-b]fluorene) molecules. Our results obtained with orca indicate that isotropic Fermi contact and anisotropic dipolar terms contribute in comparable strength, rendering the HFI markedly anisotropic. We find that the magnitude of HFI in these molecules can reach more than 100 MHz, thereby opening up the possibility of experimental detection via methods such as electron spin resonance-scanning tunneling microscopy (ESR-STM). Using these results, we obtain empirical models based on $\ensuremath{\pi}$-spin polarizations at carbon sites. These are defined by generic $s{p}^{2}$ HFI fit parameters which are derived by matching the computed HFI couplings to $\ensuremath{\pi}$-spin polarizations computed with methods such as Orca, Siesta, or mean-field Hubbard (MFH) models. This approach successfully describes the Fermi contact and dipolar contributions for $^{13}\mathrm{C}$ and $^{1}\mathrm{H}$ nuclei. These fit parameters allow to obtain hyperfine tensors for large systems where existing methodology is not suitable or computationally too expensive. As an example, we show how HFI scales with system size in $[n]\mathrm{triangulenes}$ for large $n$ using MFH. We also discuss some implications of HFI for electron-spin decoherence and for coherent nuclear dynamics.
Institutions: Donostia International Physics Center, Ikerbasque
Language: Latvian
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4382679008