This example shows how to use the pwcond.x program to calculate
the complex band structure of a system and its transmittance.
The ballistic conductance is then given by the Landauer-Buttiker formula.
In this example four systems are calculated:

1) The complex band structure of Al bulk along the (001) direction.

2) The complex band structure of a monatomic Al nanowire.

3) The complex band structure of Ni bulk along the (001) direction.

4) The transmittance of an Al wire without and with an H impurity.

NB: In order to make the tests faster, these calculations are not fully 
    converged with respect to k points, cut-off and size of the cell.

The calculation proceeds in this way:

1.a) A pw.x calculation provides the self-consistent potential of a two 
     atom tetragonal Al(001) super-cell. Al is described by norm conserving
     pseudo-potentials.

1.b) A pwcond.x calculation provides for every energy in the chosen
     region the values of the k vectors (in general complex) which 
     correspond to those energies.

2.a) A pw.x calculation provides the self-consistent potential of a 
     monatomic Al wire, described by a unit cell with a single atom.

2.b) A pwcond.x calculation provides the real and complex k vectors 
     which correspond to those energies.

3.a) A pw.x calculation provides the self-consistent potential of a two 
     atom tetragonal Ni(001) super-cell.  Ni is described by an ultrasoft
     pseudo-potential.

3.b) A pwcond.x calculation provides the real and complex k vectors which 
     correspond to those energies.

4.a) A pw.x calculation provides the self-consistent potential of 
     a perfect Al wire and of a wire (5 atoms long) with an H atom impurity.

4.b) A pwcond.x calculation gives for every energy in the chosen region 
     the transmittance at that energy for a perfect Al wire and for a wire
     with an H impurity.

 
