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<div dir="ltr">Hard to say without having a look at your system. If your system is a molecule in a (large) box then Gamma point might be enough. If you have a periodic system then you should perform a convergence test to be sure that your property of interest
converge vs the number of k-points.</div>
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<blockquote type="cite">On 20 Dec 2022, at 18:23, Rameswar Bhattacharjee <rb1820@georgetown.edu> wrote:<br>
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<div dir="ltr">Thank you, Tom. In that case, is the gamma point the best choice for me?</div>
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<div dir="ltr" class="gmail_attr">On Tue, Dec 20, 2022 at 12:17 PM Tom Demeyere via users <<a href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>> wrote:<br>
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<div dir="ltr">In periodic codes, properties (total energy is one of them) are averaged over the Brillouin zone. As a results you can’t do any assumption on how this property will change when you change k-points, it may sometime increase or sometime decrease,
I don’t think this is unusual.</div>
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<blockquote type="cite">On 20 Dec 2022, at 17:37, Rameswar Bhattacharjee <<a href="mailto:rb1820@georgetown.edu" target="_blank">rb1820@georgetown.edu</a>> wrote:<br>
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<div dir="ltr">Hi Paolo,
<div>Thank you very much for your reply and suggestion. It looks strange to me as the energy eventually converges to a high value (~0.06 Ry higher) compared to the first iteration energy. One more thing I found unusual is that (as I mentioned earlier) the total
energy obtained at the gamma point is ~0.07 Ry higher than the total energy at any other k-points. I am not much experienced with periodic calculation and never had such experience with finite methods. </div>
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<div>Rameswar</div>
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<div dir="ltr" class="gmail_attr">On Tue, Dec 20, 2022 at 11:28 AM Paolo Giannozzi <<a href="mailto:paolo.giannozzi@uniud.it" target="_blank">paolo.giannozzi@uniud.it</a>> wrote:<br>
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The energy is variational, that is: it goes down as self-consistency is <br>
approached. The energy term that makes the energy variational is however <br>
approximate and becomes exact only at self-consistency. As a consequence <br>
it may happen that at the beginning of the self-consistency the energy <br>
goes up instead of going down. Nothing to worry about as long as the <br>
energy eventually converges (monotonically from above)<br>
<br>
Paolo<br>
<br>
On 18/12/2022 19:23, Rameswar Bhattacharjee wrote:<br>
> <br>
> You don't often get email from <a href="mailto:rb1820@georgetown.edu" target="_blank">
rb1820@georgetown.edu</a>. Learn why this is <br>
> important <<a href="https://aka.ms/LearnAboutSenderIdentification" rel="noreferrer" target="_blank">https://aka.ms/LearnAboutSenderIdentification</a>><br>
> <br>
> <br>
> Hi Everyone,<br>
> I am doing a single-point calculation on a 1D polymer in QE using <br>
> PBE-PAW. However, I am seeing an issue in the SCF iteration cycles. The <br>
> first iteration seems to print the right electronic energy but from <br>
> iteration 2 the energy suddenly increases significantly and then the SCF <br>
> ends up with higher energy. I am a little confused about how to <br>
> stabilize the SCF iteration so the energy does not go up. Any <br>
> suggestions will be highly appreciated.<br>
> <br>
> I am providing the output of the first three iterations of the SCF for <br>
> deep insights.<br>
> <br>
> ------------------------------------------------------------------------------<br>
> <br>
> iteration #1 ecut= 120.00 Ry beta= 0.30<br>
> <br>
> Davidson diagonalization with overlap<br>
> <br>
> ethr =1.00E-02,avg # of iterations =2.0<br>
> <br>
> <br>
> negative rho (up, down):1.348E-04 0.000E+00<br>
> <br>
> <br>
> total cpu time spent up to now is 13.7 secs<br>
> <br>
> <br>
> total energy=-304.41586797 Ry<br>
> <br>
> estimated scf accuracy< 2.72932626 Ry<br>
> <br>
> <br>
> iteration #2 ecut= 120.00 Ry beta= 0.30<br>
> <br>
> Davidson diagonalization with overlap<br>
> <br>
> ethr =3.79E-03,avg # of iterations =1.0<br>
> <br>
> <br>
> negative rho (up, down):1.006E-04 0.000E+00<br>
> <br>
> <br>
> total cpu time spent up to now is 16.3 secs<br>
> <br>
> <br>
> total energy=-304.13553253 Ry<br>
> <br>
> estimated scf accuracy< 0.76532583 Ry<br>
> <br>
> <br>
> iteration #3 ecut= 120.00 Ry beta= 0.30<br>
> <br>
> Davidson diagonalization with overlap<br>
> <br>
> ethr =1.06E-03,avg # of iterations =6.0<br>
> <br>
> <br>
> negative rho (up, down):5.328E-05 0.000E+00<br>
> <br>
> <br>
> total cpu time spent up to now is 19.4 secs<br>
> <br>
> <br>
> total energy=-304.26340272 Ry<br>
> <br>
> estimated scf accuracy< 0.08826578 Ry<br>
> <br>
> --------------------------------------------------------------------------------------------<br>
> <br>
> Thanks<br>
> Rameswar Bhattacharjee<br>
> Georgetown University<br>
> <br>
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Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216<br>
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