Information about the Fleur Max version added

source/spex_and_fleur.rst

@@ -52,9 +52,37 @@ Furthermore, Spex needs the Fleur file "sym.out".
 
 New Fleur
 ==========
-Spex has to be compiled with ``-DFleurMax`` to make it compatible with the new Fleur "MaX" versions. 
+Spex has to be compiled with ``-DFleurMax`` to make it compatible with the new Fleur "MaX" versions.
 
-...(undocumented)...
+Also in the new Fleur "inp.xml" file there is a flag for writing out the necessary data for a Spex calculation. It can be found at the following XML-path ``/calculationSetup/expertModes/@gw``, the ``numbands`` flag can be set at ``calculationSetup/cutoffs/@numbands``.
+
+When using the input generator for fleur it is adviseable to set the option ``-kpts_gw``. This writes out additional options in the "inp.xml", which already include the settings for a second kpoint set ("kpts_gw").
+
+The following modes are available:
+
+* ``gw=0``: No output files are generated (default).
+* ``gw=1``: The files "basis.hdf" and "ecore" are written. Needed for Spex to construct the "kpts_gw" file. The broyden history is reset. The potential is not updated and Fleur stops after writing out the files.
+* ``gw=2``: All output files necessary for Spex are created and Fleur stops after one iteration (without updating the potential).
+
+The output files are:
+
+* "basis.hdf": including all information about the basis (atoms, cell, kpts, muffin tin and planewave basis information),
+* "ecore": core-electron functions,
+* "eig_gw.hdf": energies, wave-function coeffients (interstitial), wave-function coefficients (muffin tins),
+* "pot.hdf": potentials (pottot, potcoul, potx) and relevant information on the stepfunction and structure.
+
+Furthermore, Spex needs the Fleur file "sym.out".
+
+When running spex with the new Fleur you have to set the following in the spex.inp file:
+
+.. code-block:: bash
+
+   SECTION SENERGY
+     VXC CALC
+   END
+
+A short tutorial can be found at:
+http://www.flapw.de/pm/index.php?n=User-Documentation.Tutorial-DFT-Lecture-2018-DAY10
 
 Remarks about MT basis
 +++++++++++++++++++++++