van der Waals interaction in iron-chalcogenide superconductors

TL;DR

Incorporating van der Waals interactions into density functional theory significantly improves the accuracy of lattice constant predictions for iron-chalcogenide superconductors, aligning theoretical results with experimental data.

Contribution

This study demonstrates that van der Waals corrections are essential for accurate DFT modeling of FeCh superconductors, addressing previous overestimations of lattice constants and bonding strength.

Findings

van der Waals corrections improve lattice constant predictions

GGA overestimates out-of-plane lattice constants

van der Waals simulations match experimental results

Abstract

We demonstrate that the inclusion of van der Waals dispersive interaction sensibly improves the prediction of lattice constants by density functional theory in iron-chalcogenides (FeCh) superconductor compounds, namely FeSe and FeTe. We show how generalized gradient approximation (GGA) for the exchange correlation potential overestimates the out-of-plane lattice constants in both compounds when compared with experiments. In addition, GGA predicts a too weak bonding between the neutral FeCh layers, with a sensible underestimation of the bulk modulus. van der Waals corrected simulations completely solve both problems, reconciling theoretical results with experiments. These findings must be considered when dealing with theoretical predictions in FeCh compounds.