BSE with finite momentum Q
Posted: Wed Nov 01, 2023 3:04 pm
Hi all,
I did some finite center of mass momentum (Q) BSE calculations.
To my surprise the number of exchange G-vectors used in order to compute the G-sum for the electron-hole exchange matrix elements increased drastically from 23005 (for Q=0) to 111631 (for Q .ne. 0).
Furthermore I could not fully understand how the FFT grid for Q .ne. 0 (38 x 38 x 287) can get bigger than the FFT grid given by Quantum Espresso (36 x 36 x 270).
Why is this the case?
In the file "src/bse/K_driver.F" I found these 4 lines:
Why do you multiply the qindx_B_max by 4? Can you elaborate on this?
Thanks in advance.
Best,
Franz
I did some finite center of mass momentum (Q) BSE calculations.
To my surprise the number of exchange G-vectors used in order to compute the G-sum for the electron-hole exchange matrix elements increased drastically from 23005 (for Q=0) to 111631 (for Q .ne. 0).
Furthermore I could not fully understand how the FFT grid for Q .ne. 0 (38 x 38 x 287) can get bigger than the FFT grid given by Quantum Espresso (36 x 36 x 270).
Why is this the case?
In the file "src/bse/K_driver.F" I found these 4 lines:
Code: Select all
if (.not.iq==1) then
iGo_BSE=maxval((/4*qindx_B_max,qindx_X(iq,:,2)/))
iG_BSE =max(BS_n_g_exch,BS_n_g_W)
endif
Thanks in advance.
Best,
Franz