[Pw_forum] Fwd: SCF with PBE0 missing files

[Anthony Ruth]

Hello, I am trying to use version 5.0.0 to generate the band structure of a
photocathode. To do so I have been using 'vc-relax' to find the optimized
structure, copied the resulting structure to a new input file and used
'scf' to record the bands in the scratch directory, using 'bands' to print
the bands along certain points in k space, and finally using some
post-precessing to plot it all.

This method has worked correctly for my first run using the default
potential with scf which is PBE. However since this is a photocathode the
band gap is critically important, and my adviser recommended to use PBE0
which is supposed to more accurately predict the band gaps. So I took the
optimized crystal structure and used it to run an scf calculation with
input_dft="PBE0". The scf calculation seemed to work correctly, but when I
run the band calculation I get an error that says: ef not found in file. I
compared the scratch directories of the calculation using PBE and the
calculation using PBE0 and discovered that there were 4 files that were
present in the PBE scratch directory that were not present in the PBE0
directory. Two of the four files appeared to be copies of the
pseudopotentials, but the other two were data_file.xml and gvectors.dat. I
examined the data_file.xml for awhile and found that it contained the fermi
energy among many other things. gvectors.dat appears to be a byte stream,
so there is no way for me to interpret its contents.

I copied the data_file.xml from the PBE scratch directory to the PBE0
scratch directory and reran the 'bands' calculation. Lo and behold, the
calculation made it past the place that it complained about not finding the
fermi energy previously, however it could not converge during the
self-consistent calculations; probably because it was using some incorrect
settings. Also it mentioned not being able to locate a restart file; maybe
that is what gvectors.dat is for?

What I would like to know is: is this a bug? It seems to me that these
other files should have been created when using scf with PBE0, but they
just weren't. Is there a way to force these files to be created? Is it
worthwhile to try to look through the data_file.xml and make the changes
necessary to run this calculation? I noticed two pieces of information that
are incorrect in the results file because it used information from PBE
instead of PBE0, but there might be many more differences that I don't see.

-Anthony Ruth
Research Assistant at Argonne using NERSC computers.
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