# Band structure calculation {#sec:si_tuto_bs}

In this section, I show how to perform a band-structure calculation.
Copy the following input file and save it to a text file named
`si_bs.txt`.

``` shell
info.calculationType = 'band-structure'
info.savepath = 'results/si_bs'
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'
rho.in = 'results/si_scf'
```

Then pass it to RESCU and execute the program as follows

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

The band-structure calculation input file is similar to the
self-consistent calculation input except for the keywords
`info.calculationType` which value changed to `band-structure` and
`rho.in` which points to the results of the self-consistent calculation.
In this example, RESCU recognizes the face-centered cubic lattice,
defines a line sampling the irreducible Brillouin zone edges and
determines the number of k-points required to achieve the default
k-point resolution. Arbitrary k-points lines are defined via the
`kpoint.sympoints` keyword. It must be a cell array containing k-point
labels or direct coordinates, and the number of k-points can be adjusted
using `kpoint.gridn`. For example,
`kpoint.sympoints = {’G’,[0,0,0.5],’L’,[0.625,0.25,0.625]}`. The band
structure for the auto-generated line is found in
`fig:si_bs`{.interpreted-text role="numref"}. The FCC irreducible
Brillouin zone edges cannot be visited in a single continuous line, and
hence the segment U-X is thus appended to the first k-point line.

<figure>
<img src="figs/si_bs.png" id="fig:si_bs" alt="figs/si_bs.png" />
<figcaption>Band structure of bulk silicon.</figcaption>
</figure>
