[Wien] [SPAM?] Re: [SPAM?] same k vector, different eigenvectors

[Peter Blaha]

Hi,

I think this difference is numerics, probably from the mkl.

Do you use ifort + mkl (which version) ??

It would be interesting to

i) use gfortran + openblas
ii)   gfortran + self-compiled blas/lapack (from fortran sources) - will 
be very slow
iii) use compiler options with increased precision or no optimization 
(-O0). I think our default ifort options do not fully explore machine 
precision but speed. Laurence Marks may know better than me how to set 
compilation parameters with increased precision.

Are the momentum matrix elements very different or also only with 
numerical noise ?

Actually I think that they can be different, only the squared mommat 
elements should be fine (not sure about this statement).

Best regards
Peter


Am 26.04.2023 um 05:25 schrieb 曹迎迎:
> Dear Prof. Blaha,
> 
>    Thank you for your reply.
> 
>    I have checked the eigenvalue and made sure that it is not 
> degenerate. Actually, the second eigenvalue is -5.633 and differs from 
> the first value -5.833 by about 0.2 Ry.
> 
>    I undersatand the phase freedom of eigenvactor, but it seems like 
> that the difference not only came from diagonalization. After trace back 
> the output of the program, i find that the Hamiltonian matrix elements 
> are not the same. In the 2-kpt case, the Hamiltonian(HS) given by hamilt 
> in lapw1 is
> 
> ...
> 
>   -0.296635514229139      -0.296635514229139      -7.955504967907867E-003
> ...,
> 
> while in the 101-kpt case, it is
> 
> ...
> 
>   -0.296635514229139      -0.296635514229139      -7.955504967907853E-003
> ....
> 
> Is this a numerical error? Or did i do something wrong?
> 
>    In fact , I want to get finally the momment matrix case.mommat by the 
> OPTIC module. And i find that the two mommat files are different to each 
> other at the same k vector from two klists. That is why i check the 
> eigenvectors. If there is only the phase freedom in the eigenvector, 
> does it affect the momment matrix?
> 
>    Once again, thank you for your response and support. I look forward 
> to hearing back from you soon.
> 
>    Best regards, Yingying Cao
> 
> 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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