[Wien] Possible bugs in Mixer

[Peter Blaha]

Convergence could be the reason that eigenvalues differ by 10**-6 Ry and 
of course also the eigenvectors ....


Am 19.12.2025 um 19:48 schrieb Laurence Marks:
> Sorry Peter, this is not working on the DFT eigenvectors and convergence 
> is not relevant. It is doing a SVD of {YY+lamdba*SY}} to generate a 
> Penrose-Moore pseudoinverse. The vectors of an SVD are not unique within 
> a phase term.
> 
> On Fri, Dec 19, 2025 at 12:41 PM Peter Blaha <peter.blaha at tuwien.ac.at 
> <mailto:peter.blaha at tuwien.ac.at>> wrote:
> 
>     "different results":
>     I'd expect it is either not fully self-consistent for the
>     quantity/accuracy of interest (do on both computers 100 more
>     iterations), or different hardware (AVXxx, different cpu, cache, ...),
>     software like mkl-, ifort- versions or compiler options or ...
> 
> 
> 
>     Am 19.12.2025 um 17:35 schrieb Guoping Zhang:
>      > Dear Profs. Blaha and Marks and wien users,
>      >
>      > I have a question on how the new Mixer is implemented as it gives me
>      > different results on different computers.  Different results mean
>     that
>      > the eigenvalues differ by 10^-6 ry, so the wavefunctions are even
>      > worse. I am using wien2k_13 version, but there is no difference for
>      > newer versions.
>      >
>      >
>      > In FprojmemR1m.F, call DGESVD gets SVD of Vect, but SVD normally
>      > produces an arbitrary sign for U and VT for the same Vect like
>      > vect    1     1     1.7542057564
>      > vect    1     2     1.7522638412
>      > vect    2     1     1.7441856025
>      > vect    2     2     1.7425017533
>      >
>      > In one case, my U is
>      >
>      >
>      > debug3c.outputm:MMT91 U VT    1     1    -0.7091042206  
>     -0.7074733729
>      > debug3c.outputm:MMT91 U VT    1     2    -0.7051036834  
>     -0.7067399994
>      > debug3c.outputm:MMT91 U VT    2     1    -0.7051036834  
>     -0.7067399994
>      > debug3c.outputm:MMT91 U VT    2     2     0.7091042206  
>       0.7074733729
>      >
>      > Another case has
>      >
>      > debug11.outputm:MMT91 U VT    1     1     0.7091042206  
>       0.7074733728
>      > debug11.outputm:MMT91 U VT    1     2    -0.7051036834  
>       0.7067399994
>      > debug11.outputm:MMT91 U VT    2     1     0.7051036834  
>     -0.7067399994
>      > debug11.outputm:MMT91 U VT    2     2     0.7091042206  
>       0.7074733728
>      >
>      > I run 4 iterations to activate the mixer.  When I diff case.scf,
>     these two
>      > cases have no difference to the last digit,
>      >
>      > But after the mixing, it differs a lot though the total energy is the
>      > same (which is not my interest).
>      >
>      > My questions are (1) whether the new mixer finally uses some products
>      > like (U x VT) to generate the new charge density, and (2) whether you
>      > have examples that I use to verify this arbitrary sign does not
>     matter.
>      >
>      > Thank you so much in advance!
>      >
>      > Best wishes,
>      >
>      > Guoping
>      >
>      >
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>     -- 
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>     Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
>     Email: peter.blaha at tuwien.ac.at <mailto:peter.blaha at tuwien.ac.at>
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> 
> 
> -- 
> Emeritus Professor Laurence Marks (Laurie)
> Northwestern University
> Webpage <http://www.numis.northwestern.edu> and Google Scholar link 
> <http://scholar.google.com/citations?user=zmHhI9gAAAAJ&hl=en>
> "Research is to see what everybody else has seen, and to think what 
> nobody else has thought", Albert Szent-Györgyi
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-- 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Email: peter.blaha at tuwien.ac.at
WWW:   http://www.imc.tuwien.ac.at      WIEN2k: http://www.wien2k.at
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