Yambo Community Forum

Davide Sangalli wrote:Dear Feng,
I think the reason of the differences is that yambo is imposing two different cutoff on the correlation.

See the two different messages:

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[BSE-W] W size forced by symmetry to be :  65

and

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[BSE-W] W size forced by symmetry to be : 27

I do not remember why it is doing that. The subroutine responsible for it is src/bse/K_driver.F

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 !
 ! W RL size setup looking at the max index of G-G' 
 ! =========
 !
 if (.not.l_rpa_IP) then
   Max_G_m_G=eval_G_minus_G(BS_n_g_W,maxval(qindx_B(:,:,2)))
   if (BS_n_g_W/= Max_G_m_G ) then
     BS_n_g_W= Max_G_m_G
     call warning (' W size reduced due to symmetry constraints')
     call msg('s','[BSE-W] W size forced by symmetry to be :',BS_n_g_W)
   endif
 endif

Can you try to change the check into

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   if (BS_n_g_W> Max_G_m_G ) then

recompile the code and run both cases with

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BSENGBlk=  27          RL

?

The results should be identical (also you have to pay attention not to break degenerate bands when you select the band range in the BSE).

Then
i) I do not remember why the check is not just ">" but it is "/=" (it maybe an error to fix)
ii) I will test if we can avoid such reduction somehow. I think it is in principle possible. It just maybe more demanding numerically

Best,
D.

The qindx_B (and Max_G_m_G) is already different between two cases. The value maxval(qindx_B(:,:,2)) in the case with symmetry is 45 while that in the case without symmetry is 27.
This can be traced back to the difference of Xk%qtbz and q%qtbz between two cases.

BSENGBlk=  27          RL

Davide Sangalli wrote:

The qindx_B (and Max_G_m_G) is already different between two cases. The value maxval(qindx_B(:,:,2)) in the case with symmetry is 45 while that in the case without symmetry is 27.
This can be traced back to the difference of Xk%qtbz and q%qtbz between two cases.

This is why I suggested to set:

Code: Select all

BSENGBlk=  27          RL

in input. Together with the change in the code you'll have both cases running at that cutoff.

Then the check to the max value of qindx_B(:,:,2) can probably be overcome/changed.
But that would require some coding and testing.

Best,
D.