
This example shows how to use pw.x to calculate the total energy
and the band structure of four simple systems: Si, Al, Cu, Ni .

The calculation proceeds as follows (for the meaning of the cited input
variables see the appropriate INPUT_* file)

1) make a self-consistent calculation for Si (input=si.scf.{david,cg}.in,
   output=si.scf.{david,cg}.out). The number of computed bands is internally
   computed as half the number of electrons in the unit cell
   (4 in this case).

2) make a band structure calculation for Si (input=si.band.{david,cg}.in,
   output=si.band.{david,cg}).
   The variable nbnd is explicitly set = 8 so that the 4 valence bands
   and the first 4 conduction bands are calculated.  
   The list of k points given in input is the list of point where the
   bands are computed, the k-point weight is arbitrary and is not used.

3) make a self-consistent calculation for Al (input=al.scf.{david,cg}.in,
   output=al.scf.{david,cg}.out).
   Aluminum is a metal : the smearing technique is used for the 
   calculation of the Fermi energy (a value for the broadening
   degauss is provided).
   The number of bands is set to a value somehow larger that half
   the number of electrons in the cell (this is a quantity to keep under
   control and provide explicitly if the default value is too small).
   Marzari-Vanderbilt 'cold smearing' is used.

4) make a band structure calculation for Al. (input=al.band.{david,cg}.in,
   output=al.band.{david,cg}.out).
   The variable nbnd is explicitly set = 8.
   The list of k points given in input is the list of point where the
   bands are computed, the k-point weight is arbitrary and is not used.

5) make a self-consistent calculation for Cu (input=cu.scf.{david,cg}.in,
   output=cu.scf.{david,cg}.out).
   Copper is also a metal. Simple Gaussian  smearing is used
   for the calculation of the Fermi energy. K-points are automatically
   generated.

6) make a band structure calculation for Cu (input=cu.band.{david,cg}.in,
   output=cu.band.{david,cg}.out).
   The variable nbnd is explicitly set = 8.
   The list of k points given in input is the list of point where the
   bands are computed, the k-point weight is arbitrary and is not used.

7) make a self-consistent calculation for Ni (input=ni.scf.{david,cg}.in,
   output=ni.scf.{david,cg}.out).
   Nickel is a magnetic metal. A local-spin-density calculation is
   performed by specifying nspin=2 and an initial guess for the
   magnetization of each atomic species. This initial guess is used to
   build spin-up and spin-down starting charges from superposition of
   atomic charges. Methfessel-Paxton smearing of order one is used.

8) make a band structure calculation for Ni (input=ni.band.{david,cg}.in,
   output=ni.band.{david,cg}.out).

The above is done both for Davidson diagonalization (suffix
'david') and for Conjugate-gradient style diagonalization ('cg').
The code is tolerant about the presence of unnecessary information 
in the namelists so that it is not necessary to remove them from the 
input when editing the scf input to get the one for a nscf run.

