Stripe antiferromagnetic ground-state configuration of FeSe revealed by density functional theory

The magnetic ground-state configuration of iron selenide (FeSe) has been a topic of debate, with experimental evidence suggesting the stripe spin fluctuations as predominant at low temperatures, while density functional theory calculations using the exchange-correlation (XC) functional of the generalized gradient approximation (GGA) have historically predicted the antiferromagnetic (AFM) dimer configuration. In this study, we utilize the restored-regularized SCAN $({\mathrm{r}}^{2}\mathrm{SCAN})$ functional, a variant of the strongly constrained and appropriately normed (SCAN) meta-GGA, to investigate the magnetic configurations of FeSe. It is found that ${\mathrm{r}}^{2}\mathrm{SCAN}$ predicts a stripe-AFM ground-state configuration with an antiparallel spin alignment between layers. The energy difference between the parallel and antiparallel interplanar spin alignments is approximately 1.7 meV/atom, predicting a significant but previously unreported interlayer spin coupling not yet observed by experiments. The present study underscores the importance of accurate XC functionals, such as ${\mathrm{r}}^{2}\mathrm{SCAN}$, in predicting the magnetic ground-state configuration of complex materials like FeSe, highlighting its potential to predict magnetic interactions more reliably than traditional GGA functionals by adhering to exact constraints.