[Pw_forum] Fwd: SCF with PBE0 missing files

[Giuseppe Mattioli]

Dear Anthony
"band" or "nscf" calculations do not work in the case of hybrid calculations.
You can find the reason here:

 yourQE/PW/examples/EXX_example/README

There is no simple workaround. You can only struggle to draw a band structure by using the largest 
number of scf k-points affordable by your PBE0 calculation... 

HTH

Giuseppe


On Monday 15 October 2012 22:49:19 Anthony Ruth wrote:
> 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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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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