This example shows how to compute the magnetic anisotropy energy (MAE) with the
"Force Theorem" method (Phys. Rev. B 90, 205409 (2014). The system is a 3-layer
Co slab and two magnetic configurations, parallel and perpendicular to the slab
surface, are considered. 

The procedure is as follows:
1) run SCF calculation without SOC to get charge and spin moment
densities.
2) Copy them to two folders to be used for two SOC calculations
for different magnetic moment orientations - parallel and perpendicular
to the slab surface.
3) for each orientation run NSCF calculation with SOC, in the input
file one should specify in this case lforcet = .true. standing for the option
"Force Theorem".

In each case one will have already in output file the total band energy.
Their difference, eband_par - eband_perp will give the total Magnetic
anisotropy energy, MAE, in the Force theorem approximation.

To get its local decomposition over different atomic orbitals we should run
4) projwfc.x calculation for each orientation which will decompose
each band energy over atomic orbitals using PDOS. One will get two files,
eband_par.dat and eband_per.dat, containing this decomposition
for each magnetic orientation.

Taking the above difference orbital by orbital we obtain orbital-resolved MAE.

There are two new parameters to specify: lforcet and ef_0 (in projwfc.x run).
The last one should be the Fermi energy of one of NSCF calculations with SOC
and will be substracted from all the eigenvalues to produce correct
local decomposition of MAE.

Note that in order to get reliable results for the magnetic anisotropy,
you need a much denser grid of k-points than what used in this example.
