Interplay of structural properties and van der Waals forces in presence of magnet disorder in FeSe and FeTe by density-functional theory calculations

We investigate the structural origin of the iron-based superconductors FeSe and FeTe in the presence of several magnetic orders, where we focus on the competition between stripe-type anti ferromagnetism (AFM) and paramagnetic disorder (PM). Here, the PM state is implemented by using the spin-space average approach [1] in combination with constrained magnetic moments for our density-functional calculations (DFT). To predict the correct ground state in respect to the lattice parameters, we use the similarity of the AFM and PM state to transfer the correlations for specific structural properties of the AFM picture to those correlation for the PM approach.

Moreover, we found that the specific energy-volume behavior of FeSe, which looks like an “L”, leads to a weak inter-layer interaction. Therefore, we include several approaches of van der Waals (vdW) interactions to these systems to correct the Se-Se interactions and Te-Te interactions respectively. Our results show, that the additional vdW forces are as necessary to reduce the lattice mismatch between experimental and predicted values as magnetic order is [4].

[1] F. Körmann, A. Dick, B. Grabowski, T. Hickel, and J. Neugebauer, Phys. Rev. B 85, 125104 (2012)
[4] F. Ricci and G. Profetta, Phys. Rev. B 87, 184105 (2013)