This example shows how to use pw.x to calculate the total energy
and the band structure of four simple systems (Fe, Al, Cu, Ni, Fe)
in the non collinear case.

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 Fe (input=fe.scf.in,
   output=fe.scf.out). The number of computed bands is internally
   computed as equal to the number of electrons in the unit cell
   (16 in this case).

2) make a band structure calculation for Fe (input=fe.band.in,
   output=fe.band.out).
   The variable nbnd is explicitly set = 16.
   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 Fe with penalty functional
   where each component of the magnetization of the two atoms
   is constrained (input=fe.pen.in, output=fe.pen.out).
   Iron is a metal : the smearing technique is used for the
   calculation of the Fermi energy (a value for the broadening
   degauss is provided).

4) make a self-consistent calculation for Fe with penalty functional
   where the angle between the direction of the magnetization of each atom
   and the z axis is constrained; mcons(1) = cosine of this angle.
   (input=fe.angl.in, output=fe.angl.out).

5) make a self-consistent calculation for Fe with penalty functional
   where each component of the total magnetization is constrained;
   fixed_magnetization(ipol) = value of the magnetization.
   (input=fe.total.in, output=fe.total.out).

6) make a self-consistent calculation for Cu (input=cu.scf.in,
   output=cu.scf.out).
   Copper is also a metal. In this case the tetrahedron method is used
   for the calculation of the Fermi energy. K-points are automatically
   generated.

7) make a band structure calculation for Cu (input=cu.band.in,
   output=cu.band.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.

8) make a self-consistent calculation for Cu (input=cu.cg.in,
   output=cu.cg.out) with cg diagonalization.

9) make a self-consistent calculation for Cu (input=cu.diis.in,
   output=cu.diis.out) with diis diagonalization.


10) make a self-consistent calculation for Ni (input=ni.scf.in,
   output=ni.scf.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.

11) make a band structure calculation for Ni (input=ni.band.in,
   output=ni.band.out).

12) make a scf calculation of molecular oxygen relaxing the atoms.