# 9.1. Example: DOS of nickel

Let’s assume that we have accomplished a self-consistent calculation of the face-centered cubic nickel solid and that the results are in ./results/ni_lcao_scf.h5 and ./results/ni_lcao_scf.mat. One may compute the DOS of FCC nickel using the following input script.

info.calculationType = 'dos'
info.savepath = './results/ni_lcao_dos';
kpoint.gridn = [22,22,22];
kpoint.sampling = 'tetrahedron'
rho.in = './results/ni_lcao_scf';
dos.resolution = 1e-4;


Information such as structure, pseudopotentials, functional, etc. are read from rho.in. Here are some keywords which typically appear in a DOS calculation input file.

• info.calculationType determines the nature of the calculation. If it is set to dos, the eigenvalues are calculated at all non-degenerate k-points and the DOS is calculated;

• kpoint.gridn this keyword determines the fineness of the reciprocal space grid (k-point grid). It corresponds to the number of points along each reciprocal lattice vectors. Note that the accuracy is more correlated with the number of irreducible k-points than the total number of k-points. In the present example, the [22,22,22] k-grid accuracy is roughly equivalent to the [35,35,35] k-grid accuracy because the latter is more redundant than the former;

• kpoint.sampling this keyword determines the DOS shape functions. For example, if the keyword is set to gauss, then every state is smeared using a Gaussian function. In the present example, keyword is set to tetrahedron, such that the DOS is calculated using linear tetrahedral elements;

• rho.in path the the result containing the self-consistent (spin) density;

• dos.resolution sets the energy density for the DOS calculation. The default value is 10$$^{-3}$$.

The program is run as usual. For example, if the above file is saved to ni_lcao_dos, then we run it as follows.

rescu -i ni_lcao_dos


The results are found in ./results/ni_lcao_dos.mat. We can plot them typing

rescu -p ./results/ni_lcao_dos.mat


which give the plot shown in Fig. 9.1.1. You may also find the DOS data in ./results/DensityOfStates.txt.