[Pw_forum] LDA+U problem on Mac

[Mulazzi Mattia]

Dear Gabriele,

thank you for the prompt reply. Here are my comments:

>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?

I thought that the starting_ns_eigenvalue function might have worked also without the LDA+U being set to true. So I tried, but the result was the same as doing a calculation without setting the occupations.

>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.

I will try to use nosym=.true., but then, I guess, I cannot use the automatice generation of the k-points and I have to supply to the input file a list of k-points covering the whole non-irreducible Brilluoin zone. Am I right?

>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.

I am using the 4.0.5 version of QE. I tried to use the 4.1.1 (since it now suports the LDA+U for all the transition metals as well as for the rare earths), but it does not compile on  my Mac, even using the same configuration parameters that I used for the compilation of the 4.0.5 version. So for now, I gave up.
About the LDA+U, I did more testing on it both on my PC (using cygwin under WinXP) and on the Mac. The cygwin compilation recognises without problems the V pseudopotential included in the QE library. The same calculations done on the Mac require first a small modification of the tabd.f90 file. After doing that (and recompiling pw), no more "pseudopotential not yet inserted" message. However, using on the Mac the same input file that I use on the PC gives the bloody "segmentation fault". However, I found out that the segmentation fault error only appears when I use one Vanadium atom per unit cell and if I label it "V" in the ATOMIC_SPECIES name card. In this case just fixing lda_plus_u to true triggers the segmentation fault, even if the Hubbard_U is on another atom.
If I do a calculation in a larger cell with two Vanadium atoms labelled V1 and V2 (pointing to the same pseudopotential file) then I see no segmentation fault.
If I use a fictitious alloy system (say MnV or FeV in a symple cubic cell with the V atom at the 0.5 0.5 0.5 position), then I see no segmentation fault even if I label the Vanadium as "V". But if I want to calculate my system, VS2, then I have the segmentation fault. If I put a second V in the calculation and I use two labels (again V1 and V2) then no problem.
I thought it was a problem of the xc functional, but it seems it doesn't, using either PZ- or PBE-generated (ultrasoft) pseudopotentials does not solve the problem. I tried to generate the norm-conserving pseudopotentials using the ld1.x program, but PW does not recognise the pseudopotentials. I think that this last problem is related to a naming problem that Dr. de Gironcoli was explaining in the pw forum archives. I don't think it can be solved without editind the code itself.

Did any other user report on such or similar "segmentation fault" problems?

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

>Thanks,

>GS

Thank you very much,

   Mattia Mulazzi

FPR Fellow of RIKEN at Spring8
Excitation Order Research Team
1-1-1 Sayo-cho Sayo-gun, Hyogo
Japan