<div dir="ltr">Hi Axel,<br><br>I have used a much larger cutoff energy to rerun a problematic calculation. This rerun does not have the divergence problem any more. I'm going to do a few more runs to confirm this. <br>
<br>I think it's just as what you said that the effective cutoff energy becomes smaller as the cell expands. So I probably should check the convergence of stresses in my largest cell with respect to the number of plane waves. <br>
<br>btw, I did ghost states tests for my pseudo-potentials and there isn't any. <br><br>p.s., I remember to put on my affiliation this time. :) <br><br><br>Thank you very much, <br>---------------------------------------------<br>
<div dir="ltr">Hui Tang<br>Graduate Student<br>Department of Applied Physics<br>Yale University<br>Email: <a href="mailto:hui.tang@yale.edu" target="_blank">hui.tang@yale.edu</a><br>
Phone: 1-203-432-7763<br></div><br><br><br><div class="gmail_quote">On Thu, Oct 16, 2008 at 4:00 PM, Axel Kohlmeyer <span dir="ltr"><<a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">On Thu, 16 Oct 2008, Hui Tang wrote:<br>
<br>
hi hui,<br>
<br>
your cell is expanding quite a bit and your cutoff is not<br>
that large. with an expanding cell, your _effective_ cutoff<br>
becomes much smaller as the number of plane waves remains<br>
constant during a variable cell calculation. have you tested<br>
the stess tensor convergence vs. the cutoff? you basically<br>
have to figure out how many plane waves you need for a well<br>
converged stress tensor at the largest expansion of your cell<br>
and then you have to set the cutoff at the beginning so that<br>
it results in the same number of plane waves...<br>
<br>
that would explain why it works (better) if you restart.<br>
<br>
also, did you test the pseudopotentials for ghost states?<br>
<br>
cheers,<br>
axel.<br>
<br>
p.s.: please provide an affiliation. thanks.<br>
<br>
HT> Hi Nic,<br>
HT><br>
HT> 1) I have tested the pseudo-potentials (psps) with small atomic<br>
HT> separations. The pseudo-potentials give reasonable till two atoms are as<br>
HT> close as 0.8 A. When the total energy starts to diverge, which is about<br>
HT> Ionic iteration 17, the smallest inter-atomic distance is about 1.4 A. So I<br>
HT> do not think the breakdown of the psps is the trigger of this divergence of<br>
HT> the total energy, although it should be the reason for the enormous large<br>
HT> negative energies.<br>
HT><br>
HT> 2) I have tried to restart the calculation from where the divergence starts.<br>
HT> Once I did that, the first scf calculation would give a reasonable energy<br>
HT> around -41.7 Ry, and the calculation could run smoothly till the total<br>
HT> energy converges most of the times. So what I deal with this problem right<br>
HT> now is to restart calculations from where they start to have diverged total<br>
HT> energies and it's been working well. However, I hope this is not the optimal<br>
HT> way to solve this problem. :)<br>
HT><br>
HT> Thank you very much,<br>
HT> Hui<br>
HT><br>
<font color="#888888"><br>
--<br>
=======================================================================<br>
Axel Kohlmeyer <a href="mailto:akohlmey@cmm.chem.upenn.edu">akohlmey@cmm.chem.upenn.edu</a> <a href="http://www.cmm.upenn.edu" target="_blank">http://www.cmm.upenn.edu</a><br>
Center for Molecular Modeling -- University of Pennsylvania<br>
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tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425<br>
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