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<p><tt>It's confusing...</tt></p>
<p><tt>for a given grid there are two type of FFTs <br>
</tt></p>
<p><tt>the one used to transform wavefunctions, limited to G-vectors
up to Ecutwfc</tt></p>
<p><tt>and the one associated to the density/potential, up to 4*Ecutwfc
or Ecutrho</tt></p>
<p><tt>There are three grids. the Smooth one (dffts: accommodating
G-vectors up to 4*Ecutwfc), the Dense one (dfftp: accommodating
G-vectors up to Ecutrho) and the Custom one (used in exx calculations),
for a total of 2x3 = 6 combinations.</tt></p>
<p><tt>only five are actually used:</tt></p>
<p><tt>Wave: transforms wavefunction on the smooth grid (dffts)</tt></p>
<p><tt>Smooth: transforms densities/potentials on the smooth grid
(dffts)<br>
</tt></p>
<p><tt></tt>Dense: transforms densities/potentials on the dense grid
(dfftp)</p>
<p>CustomWave: transforms wavefunction on the custom grid</p>
<p>Custom: transforms densities/potentials on the custom grid.</p>
<p>The missing combination (wavefunction on the dense grid) is never
needed.</p>
<p>It would make sense to redefine the type of fft as 'Rho/Wave' but
for historical and timing-definition reasons this is not done
(yet?).</p>
<p>Have a look to FFTXlib/fft_fwinv.f90 if you want to see how
things work in detail.</p>
<p>... and actually there are three types of FFTs: Rho, Wave, and
Wave with task groups, the last one only used on the smooth grid
as invfft/fwfft('tgWave', psic, dffts)<br>
</p>
<p>stefano<br>
</p>
<p> <br>
</p>
<div class="moz-cite-prefix">On 06/11/2017 14:01, Miguel Carvajal
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:2ed9b45f-2a2f-4e3a-b8ab-e58d435256b8@Spark">
<title></title>
<div name="messageBodySection" style="font-size: 14px;
font-family: -apple-system, BlinkMacSystemFont, sans-serif;">Dear
all,
<div>can some one explain to me what is the difference of
calling </div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div style="background-color: rgb(255, 255, 255); font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; line-height: 23px; white-space: pre;"><span style="color: #af00db;">CALL</span> fwfft (<span style="color: #a31515;">'Custom'</span>, rhoc(:,ii), dfftt)</div>
</div>
<div style="background-color: rgb(255, 255, 255); line-height:
23px;">
<div style="line-height: 23px;"><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(175, 0, 219);">CALL</span>
<font face="Inconsoclasta for Powerline, Monaco, Courier
New, monospace"><span style="font-size: 15px; white-space: pre;">fwfft (</span></font><font
color="#A31515" face="Inconsoclasta for Powerline, Monaco,
Courier New, monospace"><span style="font-size: 15px; white-space: pre;">‘</span></font><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(163, 21, 21);">Wave'</span><font
face="Inconsoclasta for Powerline, Monaco, Courier New,
monospace"><span style="font-size: 15px; white-space: pre;">, rhoc(:,ii), dfftt)</span></font></div>
<div style="line-height: 23px;"><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(175, 0, 219);">CALL</span>
<font face="Inconsoclasta for Powerline, Monaco, Courier
New, monospace"><span style="font-size: 15px; white-space: pre;">fwfft (</span></font><font
color="#A31515" face="Inconsoclasta for Powerline, Monaco,
Courier New, monospace"><span style="font-size: 15px; white-space: pre;">‘</span></font><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(163, 21, 21);">Dense'</span><font
face="Inconsoclasta for Powerline, Monaco, Courier New,
monospace"><span style="font-size: 15px; white-space: pre;">, rhoc(:,ii),dfftt)</span></font><font
face="Inconsoclasta for Powerline, Monaco, Courier New,
monospace"><span style="font-size: 15px; white-space: pre;">
</span></font></div>
<div style="line-height: 23px;"><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(175, 0, 219);">CALL</span>
<font face="Inconsoclasta for Powerline, Monaco, Courier
New, monospace"><span style="font-size: 15px; white-space: pre;">fwfft (</span></font><font
color="#A31515" face="Inconsoclasta for Powerline, Monaco,
Courier New, monospace"><span style="font-size: 15px; white-space: pre;">’</span></font><span style="font-family: 'Inconsoclasta for Powerline', Monaco, 'Courier New', monospace; font-size: 15px; white-space: pre; color: rgb(163, 21, 21);">Smooth'</span><font
face="Inconsoclasta for Powerline, Monaco, Courier New,
monospace"><span style="font-size: 15px; white-space: pre;">, rhoc(:,ii), dfftt)</span></font><font
face="Inconsoclasta for Powerline, Monaco, Courier New,
monospace"><span style="font-size: 15px; white-space: pre;">
</span></font></div>
<div style="line-height: 23px;">when doing FFT on QE; as well
as the appropriate grid to be used in each instance: <b>dfft,
dfftp or dffts</b>.</div>
<div style="line-height: 23px;">I have some ideas but not a
full understanding of it.</div>
<div style="line-height: 23px;">Best regards,</div>
</div>
</div>
<div name="messageSignatureSection"><br>
<div class="matchFont"><span style="orphans: 2; widows: 2;
font-size: 14px; font-family: -apple-system,
BlinkMacSystemFont, sans-serif;">Lic. Miguel Carvajal -
Instituto Balseiro - Bariloche</span></div>
<div class="matchFont">
<div style="orphans: 2; widows: 2; font-size: 14px;
font-family: -apple-system, BlinkMacSystemFont, sans-serif;">National
Atomic Energy Comission</div>
<div style="orphans: 2; widows: 2; font-size: 14px;
font-family: -apple-system, BlinkMacSystemFont, sans-serif;">[+54]
2944782429 (tel) / krvajal.miguel (skype)</div>
<div style="orphans: 2; widows: 2; font-size: 14px;
font-family: -apple-system, BlinkMacSystemFont, sans-serif;">LinkedIn:
<a href="https://www.linkedin.com/in/krvajal/"
style="font-size: 14px; font-family: -apple-system,
BlinkMacSystemFont, sans-serif;" moz-do-not-send="true">in/krvajal</a></div>
</div>
</div>
<br>
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