This demonstrates the usage of the basis connection and curvature in
a python subroutine to caluclate all terms of the Berry curvature.
It tries to replicate Wang, PRB 74, 195118 (2006), Fig, 4 and 6.

Note, that we use a sign which accords to A= -i <u|grad u>
in contrast to Wang. However, in this way we can reproduce the sign
of their published results (Fig. 6 shows -Fz)


It will not be exactly the same.
The result Fig. 4 depends on the chosen gauge in general
but not here, since there is only one atom sitting at 000.
(Look into run for options.)

First execute

     fscuts.py
      
and then

     run

load results via

     xfbp curvature_bands.xpy

and
     xfbp curvature_density.xpy
