From now on keep the number of k-points and the wrap around errors fixed (i.e. try to use always the same ratio between the value which avoids all wrap around errors and the actual FFT-mesh). Test how many bulk and vacuum layers are necessary to get a reasonable surface energy, and a reasonable converged force on the first (and possibly second) slab layer.

*Mind:* Do not change more than one parameter from one calculation to the next
calculation. It is almost impossible to compare two calculations which differ
in the number of k-points and in the size of the supercell.
Be very careful about the FFT-meshes: If you increase the size
of the supercell without increasing the size of the FFT mesh the results
do *not* improve. Actually results get even worse in this case because
the wrap around error increases.

Mon Mar 29 10:38:29 MEST 1999