First principle calculation of the structural and electronic properties of cobalt using quantum espresso package

Abstract

In this thesis, the electronic structural properties of Cobalt (Co) was investigated with the density functional theory by using Quantum Espresso Package. The generalized gradient approximation (GGA) was used to compute the exchange correlation energy. The total energy of Cobalt is performed as a function of cutoff energy and Monk Horst- pack grid size. The results show that the total energy per cell is monotonically decreasing with increasing cutoff energy and converged 50Ry plane wave cutoff energy and the ground state energy had its minimum at -596.86253968 Ry. The total energy of Co per cell has converged at 8×8×8 k-point grids with a ground state energy of -593.47698056 Ry. Besides, the optimized lattice constants of bulk Co have been determined to be a = 4.7 Bohr , c = 7.59168, and c/a = 1.615251 with respect to our computational calculation. The experimental values of bulk HCP cobalt is (a = 4.743212 Bohr, c = 7.691185 Bohr, and c/a = 1.622). The lattice constant determined using DFT calculation is compatible with an experimental result by an error of 1.29%. Moreover, different smearing calculations were made and it was observed that both mv and mp are much less dependent upon degauss and allow for faster convergence than simple Gaussian broadening. Finally, the band structure and density of state of HCP cobalt was computed. The band structure calculation shows that there is overlap between the conduction band and the valance band. This clearly shows that Co is purely metallic and zero band gap material. The density of state also shows that there is no discontinuity before and after the Fermi Level. The density of state is continuous and there is no an insulating regime