it's in SUBROUTINE realspace_grid_init in FFTXlib/src/file fft_types.f90
!
! ... calculate the size of the real-space dense grid for FFT
! ... first, an estimate of nr1,nr2,nr3, based on the max values
! ... of n_i indices in: G = i*b_1 + j*b_2 + k*b_3
! ... We use G*a_i = n_i => n_i .le. |Gmax||a_i|
!
dfft%nr1 = int ( sqrt (gcutm) * sqrt (at(1, 1)**2 + at(2,
1)**2 + at(3, 1)**2) ) + 1
dfft%nr2 = int ( sqrt (gcutm) * sqrt (at(1, 2)**2 + at(2,
2)**2 + at(3, 2)**2) ) + 1
dfft%nr3 = int ( sqrt (gcutm) * sqrt (at(1, 3)**2 + at(2,
3)**2 + at(3, 3)**2) ) + 1
stefano
On 27/02/25 20:11, Dyer, Brock wrote:
Hello all, I have been working quite a bit lately on automating my QE
workflow, and as part of that workflow I check the automatically
calculated FFT grid sizes for the level of theory that I have been
using in order to improve my parallelization.
I have tried tracing down and reading the code that calculates the FFT
grid sizes, however I cannot find/understand the actual code to
calculate the grid sizes. My current understanding is that the initial
parameters to calculate the grid size are 'ecutwfc' and/or 'ecutrho',
and the unit cell size, and then there seems to be some more math, and
perhaps at the end the final dimensions get calculated in 'fft_ggen.f90'.
What I am looking for ideally is a mathematical formula that includes
all of the input parameters and operations required to calculate the
FFT grid sizes so that I can implement it into my workflow and
hopefully not have to run double calculations to properly parallelize.
Thanks in advance for the help!
Brock Dyer, Ursinus College Class of 2025
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_______________________________________________________________________________
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worldwide who are victims of terrorism, military aggression, and indiscriminate
warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list users@lists.quantum-espresso.org
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