[QE-users] Initial Guess Suggestion

[Lucas Nicolás Lodeiro Moraga]

Hello all!
I am a QE user since 2017, I start using the 5.4 version, and now I am
using the 6.1 version. I saw that when you use the starting pot/wfc
options, there are some cases where these options does not work very well,
and some obvious changes can be done. First of all, I do not know if these
changes are already implemented in the new versions, I apologize if was
done in the new versions.
For GGA calculation there are 4 combinations of starting guess: the
default, a random/atomic wfc and density. The full read guess with wfc and
density. Read density only. This three are ok. The fourth is only reading
the wfc...
When the wfc is the only reading one, the program use the read wfc, and a
random/atomic density. This situation is not useful because the read wfc
does not match with the random density (and with the "random potential")
and there is not any improvement over the calculation. I think (I do not
know if this implementation is easy) for this case the density must be
created using the wfc, because if the wfc is near the minimum, the density
is near the minimum too.
Another case is for hybrid functionals, for the starting wfc and starting
wfc/density cases, I think some changes could be done. The typical hybrid
calculation starts with a GGA calculation. If you use the read starting
guess from another hybrid calculation, this guess is far away of GGA
minimum, but near the hybrid minimum, and the first GGA calculation breaks
the "good guess" to a GGA solution. If in these cases the first step was
the fock matrix calculation, we can get an upgrade, because the full
potential was very similar to those to the read wfc/density.

Regards!
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