
WARNING: BEFORE RUNNING A CALCULATION FOR PRODUCTION,
TEST THE PSEUDOPOTENTIAL AND BASIS SETS, AND PERFORM
THE CONVERGENCE TESTS FOR THE MESH CUTOFF AND THE SAMPLING IN K-SPACE.

IN THE PRESENT EXAMPLES, AND IN ORDER TO SPEED THE CALCULATIONS,
WE PROVIDE SOME VALUES OF THESE PARAMETERS FOR YOU.

WE DO NOT GUARANTEE THAT THE VALUES OF THESE PARAMETERS ARE CONVERGED.

---------------------------------------------------------------------
Pablo Aguado-Puente (2007)
pablo.aguado@unican.es
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* Look at the input file, MgO.fdf, and study the different variables.
Pay special attention to the new variables in this example, and
check their meaning in the User's Guide:
   BandLineScale
   %block BandLines

You can check the path chosen in k-space (%block BandLines) in this
example at the websites mentioned in the Al example.

Run Siesta:

    siesta < MgO.fdf > MgO.out 

* Siesta writes the bands information in a file called systemlabel.bands,
in this case MgO.bands. Take a look at this file with a text editor:

  - The first line of the file is the energy of the Fermi level.
  - The numbers in the second line are minimum and maximum of the path
    chosen in k-space.
  - The numbers in the third line are the minimum and maximum energies
    of the bands diagram.
  - The numbers in the fourth line are the numers of orbitals/bands 
    calculated, spin restricted (=1) or unrestricted (=2), and the
    total number of k-points where the bands have been calculated.
  - Then the bands are written in each k-point. Check that for each 
    k-point (first column) there are as many bands as the first number
    in the fourth line.
  - At the end of the file the high symmetry k-points are written.
    First the number of these points, and then in two columns, the 
    position in the path and their name.

* The file systemlabel.bands can be processed with gnubands:

  gnubands < MgO.bands > bands.dat

and the resulting bands.dat file plotted with:

    gp bands.gplot

The result is a plot with the band diagram of MgO. 

You can now discuss whether this system is an insulator, a
semiconductor or a metal.

What's the value of the gap?
Compare it with the experimental value 7.8 eV. 
Is it direct or indirect? 


