Evolution of the electronic structure and structural properties of BaFe2As2 at the tetragonal-collapsed tetragonal phase transition

Density functional theory generalized gradient approximation has been used to calculate the electronic and structural properties of BaFe2As2 compound up to 56 GPa by using Quantum Espresso code. Structural properties like bulk modulus, Fe-As bond length, and As-Fe-As bond angles have been investigated by pressure especially near the tetragonal to collapsed tetragonal (T-cT) structural phase transition. This study shows considerable changes of these parameters in the cT phase, which happens near our calculated critical pressure, P-c = 24 +/- 2 GPa. Electronic band structure and its orbital-resolved, total and partial density of states and Fermi surfaces have been investigated in this pressure range. The four hole-and electron-like bands have been decreased to only one electron-like band at the T-cT phase transition. The Fermi surface topology changes from two-dimensional cylinders to three-dimensional pockets in the cT phase. The sharp peaks of total and partial density of state are broadened by pressure and the width of conduction electron states increases continuously to about 2 eV at 56 GPa. The Fe3d states have the main contribution at the density of states at Fermi level, which decreases suddenly near P-c. The considerable changes in these parameters in the cT phase indicate completely different electronic properties of this compound in high pressures relative to the tetragonal phase at ambient pressure. (C) 2015 Elsevier B.V. All rights reserved.