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<p>it's in SUBROUTINE realspace_grid_init in FFTXlib/src/file
fft_types.f90<br>
</p>
<p> !<br>
! ... calculate the size of the real-space dense grid for
FFT<br>
! ... first, an estimate of nr1,nr2,nr3, based on the max
values<br>
! ... of n_i indices in: G = i*b_1 + j*b_2 + k*b_3<br>
! ... We use G*a_i = n_i => n_i .le. |Gmax||a_i|<br>
!<br>
dfft%nr1 = int ( sqrt (gcutm) * sqrt (at(1, 1)**2 + at(2,
1)**2 + at(3, 1)**2) ) + 1<br>
dfft%nr2 = int ( sqrt (gcutm) * sqrt (at(1, 2)**2 + at(2,
2)**2 + at(3, 2)**2) ) + 1<br>
dfft%nr3 = int ( sqrt (gcutm) * sqrt (at(1, 3)**2 + at(2,
3)**2 + at(3, 3)**2) ) + 1<br>
<br>
</p>
<p>stefano</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 27/02/25 20:11, Dyer, Brock wrote:<br>
</div>
<blockquote type="cite" cite="mid:PH7PR22MB3661BC69230771632662EA09CFCD2@PH7PR22MB3661.namprd22.prod.outlook.com">
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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. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
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'. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
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.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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Thanks in advance for the help!</div>
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<br>
</div>
<div id="Signature" style="color: inherit;">
<p>Brock Dyer, Ursinus College Class of 2025</p>
<p><br>
</p>
</div>
<br>
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