MgB2 under pressure and plane strain: a DFT study

Full potential density functional theory (DFT) calculations have been performed for the MgB2 superconductor. Results show that applying positive (negative) pressure leads to a decrement (increment) in the DOS at the Fermi level that this calculations suggest a decrement in TcTc under application of positive pressure. In the Γ–AΓ–A path of momentum space, the band which has the dominant role in conduction properties, moves upward when c increases or a decreases, and moves downward when c decreases or a increases. By relaxation of the system under the plane strain, we have studied the behavior of axial lattice parameter c. Our results show that changes in the axial lattice constant c is one third of the changes of planar lattice constant a  . It has been seen that by applying small in-plane strain (tensile), DOS at the Fermi level increases, but it decreases for higher applied strain. For the negative in-plane strain (compression), DOS decreases monotonically at the Fermi level. It can be seen that tension makes the electronic bands to move downward in the Γ–AΓ–A direction of the reciprocal lattice, but by compression, they move upward. Based on these results, it can be concluded that by applying small tension, one can enhance TcTc in MgB2 compound.