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<p>Dear Dyer,</p>
<p> you are right... the factor of two you find is the difference
between the radius and the diameter of a sphere.</p>
<p> <br>
</p>
<p> the bit of code in FFTXlib/src/fft_type.f90 I pointed to
earlier defines the ranges nr1,nr2,nr3 of a parallelepiped box
that contains the G-sphere of sqrt(gcutm) radius. <br>
</p>
<p> these are then passed to grid_set( dfft, bg, gcutm, dfft%nr1,
dfft%nr2, dfft%nr3 ) where the actual size is determined in three
nested loops that range from - the estimated limit to + the
estimated limit<br>
</p>
<p> DO k = -nr3, nr3<br>
DO j = -nr2, nr2<br>
DO i = -nr1, nr1</p>
<p><br>
</p>
<p> where the maximum ACTUAL absolute index values are set as
nb(1),nb(2),nb(3), which should coincide with nr1,nr2,nr3 if they
were computed properly, and finally set the grid dimensions as <br>
</p>
<p><br>
</p>
<p> nr1 = 2 * nb(1) + 1<br>
nr2 = 2 * nb(2) + 1<br>
nr3 = 2 * nb(3) + 1<br>
<br>
</p>
<p>stefano</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 02/03/25 06:04, Dyer, Brock wrote:<br>
</div>
<blockquote type="cite" cite="mid:PH7PR22MB3661A855AAC32997B33845DBCFCE2@PH7PR22MB3661.namprd22.prod.outlook.com">
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<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
I've been tracing down all the variables that are required to
generate a good FFT grid, and I seem to be off by a factor of 2
in the end. I can't quite figure out what the issue is, but my
guess may be that while I am storing 'ecutwfc' in Rydbergs there
is a conversion to Hartrees somewhere in the code that I haven't
seen yet. </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);">
My current process looks like this (with some values from a run
I had recently so I can compare):</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);">
ecutwfc = 100 Ry</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
Ecutrho = 400 Ry</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="line-height: 24px; font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
# Unit cell dimensions, given in Bohrs</div>
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v1 = [44.09733757, 0.0, 0.0]</div>
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v2 = [0.0, 44.09733757, 0.0]</div>
<div class="elementToProof" style="line-height: 24px; font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
v3 = [0.0, 0.0, 44.09733757]</div>
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<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);">
alat = sqrt(v1[0]**2 + v1[1]**2 + v1[2]**2)</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
tpiba = (2.0 * pi) / alat</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
gcutm = ecutrho / (tpiba**2)</div>
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<br>
</div>
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at = [v1/alat, v2/alat, v3/alat]</div>
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<br>
</div>
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nr1 = int(sqrt(gcutm) * sqrt(at[0][0]**2 + at[0][1]**2 +
at[0][2]**2)) + 1</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
nr2 = int(sqrt(gcutm) * sqrt(at[1][0]**2 + at[1][1]**2 +
at[1][2]**2)) + 1</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
nr3 = int(sqrt(gcutm) * sqrt(at[2][0]**2 + at[2][1]**2 +
at[2][2]**2)) + 1</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
These last lines are where I've noticed the problem. From
looking at the output of my run with the given cell sizes, I
expect an FFT grid of 288x288x288, however if I were to run this
code (and the code that checks if it's a good size) I'd get an
FFT grid that is only half that. I'd love some advice on this if
it is at all possible. I also can send some more formatted code
if it would help (I decided to cut down the python code so it
looked a bit more like the original f90 code).</div>
<div class="elementToProof" style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<hr style="display: inline-block; width: 98%;">
<span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"><b>From:</b> users
on behalf of Stefano de Gironcoli<br>
<b>Sent:</b> Thursday, February 27, 2025 2:50 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a><br>
<b>Subject:</b> Re: [QE-users] Details of Automatic FFT Grid
Size Calculation </span>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<p style="margin-top: 0px; margin-bottom: 0px;">it's in SUBROUTINE
realspace_grid_init in FFTXlib/src/file fft_types.f90</p>
<p style="margin-top: 0px; margin-bottom: 0px;"> !<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 style="margin-top: 0px; margin-bottom: 0px;">stefano</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<div>On 27/02/25 20:11, Dyer, Brock wrote:</div>
<blockquote>
<div style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
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 style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div 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 style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div 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 style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
Thanks in advance for the help!</div>
<div style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div id="x_Signature" style="color: inherit;">
<p style="margin-top: 0px; margin-bottom: 0px;">Brock Dyer,
Ursinus College Class of 2025</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
</div>
<br>
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<pre class="moz-quote-pre" wrap="">_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare.
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Quantum ESPRESSO is supported by MaX (<a class="moz-txt-link-abbreviated" href="http://www.max-centre.eu">www.max-centre.eu</a>)
users mailing list <a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>
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