Impact of Coulomb interactions on the phase transition and electronic structure of Ba2N electride under pressure: A DFT+U+V approach

Abstract

We study the electronic structure of the low-dimensional electride Ba${}_2$N to resolve discrepancies between density functional theory (DFT) predictions and experimental observations of pressure-induced phase transitions. According to the DFT calculations, there is no transition from the $P\bar{3}m1$ symmetry metallic phase to the $I\bar{4}2d$ phase, while in the experiment this transition is observed at 7 GPa. Using the density functional perturbation theory (DFPT) method, we have calculated the $U$ and $V$ parameters of the on-site and inter-site Coulomb interactions. Subsequently, applying the DFT+U+V method, we have found that taking into account the local and non-local interactions allows us to reproduce the metal-semimetal transition and to establish the energy balance that provides the structural transformation from $P\bar{3}m1$ to $I\bar{4}2d$ observed in the experiment. Therefore, the Coulomb interactions between the electrons, located predominantly in the interstitial voids, are important and lead to a qualitative change in the band structure and to the opening of an indirect gap in the subband corresponding to the electride states.