electronic and structural properties of nickel using density functional theory (quantum espresso)

Abstract

Nickel is a metal which is widely distributed in nature; and it is found in animals, plants, and soil. The density functional theory (DFT) simulation tools were employed to investigate energies, magnetization and geometrical structure of nickel (Ni) using quantum ESPRESSO package. A number of convergence test were performed, to establish the optimal value of various parameters in the numerical calculations. Firstly, the total minimum energy of nickel per atom is calculated as a function of cut-off energy, and k-points. Secondly, the optimal lattice constant and the magnetic ordering were calculated for bulk nickel. Here to find the equilibrium lattice constant of nickel, the total energy calculation with a series possible parameters of lattice constant have been performed. Moreover, the total magnetization of an atom is computed as a function of smearing(Marzari-Vanderbilt). In addition to these, Fermi-Dirac function was employed to describe the probability of electronic state occupations. Also the calculations were repeated with Gaussian, Marzari-Vanderbilt and MethfesselPaxton functions. The total minimum energy per atom is monotonically decreasing with increasing cutoff energy due to variational principle. However, this trend can not be predicted from increasing the k-point sampling. The computational value of the equilibrium lattice constant is 6.47 Bohr. This result is in good agreement with experimental value. Furthermore, the negative magnetization observed in low fields has been ascribed to two oppositely ordered ferromagnetic super exchange interactions. Moreover, the convergence in cold smearing is very fast than Fermi-Dirac smearing.