[Pw_forum] Charge ordering with QE

[Gabriele Sclauzero]

Dear Mattia,

Mulazzi Mattia wrote:
> In order to calculate the electronic structure of an orbitally-ordered  
> system I think I have to use a supercell and specify different  
> occupation numbers for the different Vanadium sites. The problem is  
> that I don't know how to do that. I tried specifying the  
> starting_ns_eigenvalue variable on different sites, but the converged  
> calculation is identical to the calculation with  
> starting_ns_eigenvalue left unspecified. In the INPUT_PW it is written  
> that the occupation matrices can be specified only when the LDA+U  
> scheme is used.

I don't understand a thing: starting_ns_eigenvalue is used only on the species on which 
you put +U (i.e. Hubbard_U(?)>0), so if you cannot not use LDA+U for V with your QE 
installation, how could you say that using starting_ns_eigenvalue does not change the result?

One other important point is that occupations are symmetrized according to the symmetry of 
the system. So that, perhaps, retrying after breaking some symmetry or using nosym=.TRUE. 
may change something.

> However, I cannot use the LDA+U on my system (Mac OS X 10.5.6) because  
> every time I use the Vanadium pseudopotential (either the one I  
> generated, ether the one on the QE database) I find a "segmentation  
> fault" that I  cannot solve. BTW, the segmentation fault error does  
> not appear for Co or Fe or Ni pseudopotentials.

Which version of QE are you using?
Please check if the Vanadium case has already been inserted in tabd.f90 and 
set_hubbard_l.f90 files.
If not pw.x should stop with an error message like
  "pseudopotential not yet inserted"
before causing any segmentation fault.
 From version 4.1 on, LDA+U should be working with any of the transition metal elements.
If you have previous versions, you can easily get it working modifying those two files.

Please report to us if the problem persists in v4.1 and if it is reproducible.

Thanks,


GS

> 
> Thanks everybody for the help,
> 
>      Mattia Mulazzi
> 
> 
> FPR Fellow of RIKEN at Spring8
> Excitation Order Research Team
> 1-1-1 Sayo-cho Sayo-gun, Hyogo
> Japan
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-- 


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| Gabriele Sclauzero, PhD Student                  |
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