# Density of states calculation {#sec:si_tuto_dos}

In this section, I show how to calculate the density of states (DOS) of
bulk silicon. In principle, all I have to do is set the keyword
`dos.status` to true and perform a self-consistent calculation. In
practice, the DOS is calculated non-self-consistently as the number of
k-point required to converge the DOS is much higher than the number of
k-point required to converge the ground state density. To perform a DOS
calculation, copy the following input file and save it to a text file
named `si_dos.txt`.

``` shell
info.calculationType = 'dos'
info.savepath = 'results/si_dos'
atom.element = [1 1]
atom.xyz = 10.25*[0 0 0;0.25 0.25 0.25]
domain.latvec = 10.25*[0.0 0.5 0.5;0.5 0.0 0.5;0.5 0.5 0.0]
domain.lowres = 0.5
element.species = 'si'
element.path = './Si_TM_LDA.mat'
kpoint.gridn = [10,10,10]
rho.in = 'results/si_scf'
```

Then pass it to RESCU and execute the program as follows

``` shell
rescu -i si_dos.txt;
```

The DOS calculation input file is similar to the self-consistent
calculation input file. The differences are highlighted in blue.
`info.calculationType` is set to `’dos’` and `rho.in` points to the
results of the self-consistent calculation so that RESCU reads the
ground state electronic density. `info.savepath` is modified not to
overwrite the self-consistent results and the k-sampling is increased.
In the present case, a
10$\times$`<!-- -->`{=html}10$\times$`<!-- -->`{=html}10 grid is
sufficient since the default sampling method is the linear tetrahedron
method and the bands of silicon are relatively smooth.

# Plot results {#sec:si_tuto_plotresults}

RESCU automatically plots certain results (e.g. band structures, DOS,
projected DOS). It create a MATLAB figure that can be modified (title,
axis, etc.) subsequently. To plot the density of states, use the `plot`
flag to point RESCU to the data.

``` shell
rescu -p results/si_dos.mat results/si_dos.png;
```

The second input (`results/si_dos.png`) is optional and it determines
the name and the file format of the figure. The DOS obtained from the
example in section [3](#sec:si_tuto_dos) is found in
`fig:si_dos`{.interpreted-text role="numref"}.

<figure>
<img src="figs/si_dos.png" id="fig:si_dos" alt="figs/si_dos.png" />
<figcaption>DOS of bulk silicon</figcaption>
</figure>
