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<p>From the WIEN2k usersguide [1] and previous posts in the mailing
list [2,3], I glean that <font color="#ff0000">xc</font><font
color="#33cc00">pot</font>3 is the <font color="#ff0000">exchange-correlation</font>
<font color="#33cc00">potential</font> in the interstitial region
[4].</p>
<p><br>
</p>
<p><font color="#ff6600">I</font><font color="#3333ff">FFT</font>
likely refers to the <font color="#ff6600">upper limit of the
summation</font> [5] of a <font color="#3333ff">fast Fourier
transform (fft)</font> [6,7]. So by increasing the IFFTx,y,<font
color="#cc33cc">z</font> values in the x, y, or <font
color="#cc33cc">z</font> direction or the multiplicative
enhancement factor, I think you can expect that the fft error
reduces for the exchange-correlation potential but at the cost of
a slow calculation due to the increase in the number of fft
summation terms.<br>
</p>
<p><br>
</p>
<p>[1]
<a class="moz-txt-link-freetext" href="http://susi.theochem.tuwien.ac.at/reg_user/textbooks/usersguide.pdf">http://susi.theochem.tuwien.ac.at/reg_user/textbooks/usersguide.pdf</a><br>
</p>
<p>[2]
<a class="moz-txt-link-freetext" href="https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg07410.html">https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg07410.html</a><br>
[3]
<a class="moz-txt-link-freetext" href="https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg07166.html">https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg07166.html</a></p>
<p>[4] <a class="moz-txt-link-freetext" href="http://susi.theochem.tuwien.ac.at/lapw/index.html">http://susi.theochem.tuwien.ac.at/lapw/index.html</a><br>
</p>
<p>[5] <a class="moz-txt-link-freetext" href="http://www.columbia.edu/itc/sipa/math/summation.html">http://www.columbia.edu/itc/sipa/math/summation.html</a></p>
<p>[6] <a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Fast_Fourier_transform">https://en.wikipedia.org/wiki/Fast_Fourier_transform</a></p>
<p>[7]
<a class="moz-txt-link-freetext" href="https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg05582.html">https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg05582.html</a><br>
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<div class="moz-cite-prefix">On 5/15/2019 10:49 AM, AJAY SINGH VERMA
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:BM1PR01MB09648B9AF0BEB082BC76377DE2090@BM1PR01MB0964.INDPRD01.PROD.OUTLOOK.COM">
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<div style="font-family: Calibri, Helvetica, sans-serif;
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Dear Sir, <br>
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<div style="font-family: Calibri, Helvetica, sans-serif;
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<br>
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<div style="font-family: Calibri, Helvetica, sans-serif;
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I am facing some problem in structural optimization. When i
perform my calculation with variable volume percentage from -6
to 6 with difference 1. In starting the complete scf cycle run
but when 6% volume term comes error massage shown
<b>"ifft so small in xcpot3".</b> As per the previous mailing i
change ifft parameter from 75 75 75 to 0 0 0 and enhancement
factor from 1.0 to 2.0.in in0 file after that complete cycle run
and curve is completely plotted.
<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
I have some questions:- <br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
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What is the effect of this change?</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
does it change the value of crystal parameter?<br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
what it represent? </div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
<br>
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<div style="font-family: Calibri, Helvetica, sans-serif;
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Thanking you <br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);">
Ajay Singh Verma<br>
</div>
</blockquote>
<blockquote type="cite"
cite="mid:BM1PR01MB09648B9AF0BEB082BC76377DE2090@BM1PR01MB0964.INDPRD01.PROD.OUTLOOK.COM"></blockquote>
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