<div dir="ltr"><div>Dear Stefano<br><br></div>Thank you very much for your reply. I answer to your questions below.<br><div class="gmail_extra"><br><div class="gmail_quote">2016-12-28 16:29 GMT+01:00 Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it" target="_blank">degironc@sissa.it</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Pablo Garcia Risueño<br>
<br>
I'm not sure I understand the problem.<br>
the two final positions for ecut=30 are identical to my eyes.<br>
the two final positions for ecut=60 differ by about 10-5 A. !<br>
If the property you are interested in depends so strongly on the<br>
atomic positions you better learn how to live with it. Even assuming<br>
that you are using perfect xc functional, perfect pseudopotentials and<br>
converged cutoff and k-points (which likely you don't), your<br>
calculation is neglecting zero point energy, thermal expansion,<br>
quantum nature of H motion, ...<br>
<i><br></i></blockquote><div><i>Yes, my concern is not that the results are not perfect (of course DFT makes non-negligible errors). My concern is that fully identical input files run in the same machine and with the same executable provide different results.</i><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
As for your specific question. In principle if you tighten enough<br>
the convergence the minima should tend to converge toward a common<br>
value. However the stopping criteria will make the two calculations<br>
stop as soon they are satisfied. In your case as soon as each force<br>
component is lower than 10-6 Ry/au and the energy does not change more<br>
that 10-8. Did the calculation complete ? 10-8 for the energy is<br>
easily reachable but 10-6 for the forces looks to me very demanding.<br>
<i><br></i></blockquote><div><i>Yes, the calculations do finish. I read 'Begin final coordinates' (...) and 'JOB DONE' at the end of the output files. My system is very small (just 26 atoms and 56 electrons).</i><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Anyhow... even if the relaxation did complete successfully two<br>
equivalent calculations may still differ. If you run your calculations<br>
with exactly the same input on exactly the same machine with exactly<br>
the same mpi setup the results should be identical </blockquote><div><i>This is exactly what I do.</i><br> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">..but why doing<br>
twice exactly the same calculation ?. </blockquote><div><i>The 'relax' calculation is the first step of a complicated process. I run two different calculations because the 6th step of the process is different. I obtained very different results at the end of the full process; then I tried to trace back the differences. And then I saw that despite the fact that the 1st step is identical for two different runs, the results of the 1st step are different. This made me think that there might be a bug, or a wrong parameter in my input files.</i><br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">If however you change anything<br>
in the input (Davidson vs CG, starting wavefunction options, mixing<br>
mode, BFGS-related parameters) or parallel computational setup the<br>
relaxation history will be slightly different and the final<br>
configurations will differ by a certain amount allowed by the<br>
tolerance defined by your stopping criteria.<br></blockquote><div><i>I changed nothing, this is why I am surprised with the results...</i> <br></div><div><br><br></div><div>Thank you very much for your attention. Best regards.<br></div><div><br><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
HTH<br>
<span class="HOEnZb"><font color="#888888"><br>
stefano<br>
</font></span><div class="HOEnZb"><div class="h5"><br>
Quoting Pablo García Risueño <<a href="mailto:garcia.risueno@gmail.com">garcia.risueno@gmail.com</a>>:<br>
<br>
> Dear professor<br>
><br>
> Thank you very much for your reply. The differences are important in this<br>
> case, my final calculated quantities are very sensitive to these optimized<br>
> positions. Should I change any of the ***conv_thr variables, or other<br>
> variable, to have the same result for same inputs?<br>
><br>
> Is there any random number in the algorithm of relax calculations, can we<br>
> be sure that different outputs with the same input are not due to any bug?<br>
><br>
> Thank you very much. Best regards.<br>
><br>
> 2016-12-28 14:10 GMT+01:00 Paolo Giannozzi <<a href="mailto:p.giannozzi@gmail.com">p.giannozzi@gmail.com</a>>:<br>
><br>
>> The differences you find are very small. Nothing to worry about in my<br>
>> opinion.<br>
>><br>
>> By the way: Davidson diagonalization is typically faster than CG; do not<br>
>> specify incompatible options in K_POINTS (gamma or automatic, not both;<br>
>> gamma should be used unless you have a good reason not to)<br>
>><br>
>> Paolo<br>
>><br>
>> Il 28/dic/2016 01:46 PM, "Pablo García Risueño" <<a href="mailto:garcia.risueno@gmail.com">garcia.risueno@gmail.com</a>><br>
>> ha scritto:<br>
>> ><br>
>> > Dear Espresso community<br>
>> ><br>
>> > I have one problem that is important for me; it is somewhat surprising.<br>
>> I run geometry optimization (relax) calculations with pw.x with identical<br>
>> input files, and I obtain rather different final coordinates. The problem<br>
>> does not happen if ecutwfc is 30, but it does appear for cutoffs of 60, 80<br>
>> or 90. Below one can see the exact input file, and examples of the<br>
>> difference between the final coordinates for both runs (both run with<br>
>> identical input) for given cutoffs.<br>
>> ><br>
>> > Could anybody give me a clue on the origin of the problem, and how to<br>
>> solve it?<br>
>> ><br>
>> > Thank you very much. Best regards.<br>
>> ><br>
>> ><br>
>> ><br>
>> > Input file:<br>
>> ><br>
>> ><br>
>> ><br>
>> > &CONTROL<br>
>> ><br>
>> > calculation = 'relax',<br>
>> ><br>
>> > restart_mode = 'from_scratch',<br>
>> ><br>
>> > prefix='',<br>
>> ><br>
>> > outdir = './',<br>
>> ><br>
>> > pseudo_dir = '/path_xxx/PP/',<br>
>> ><br>
>> > forc_conv_thr = 1.0D-6 ,<br>
>> ><br>
>> > etot_conv_thr = 1.0D-8 ,<br>
>> ><br>
>> > /<br>
>> ><br>
>> > &system<br>
>> ><br>
>> > ibrav = 0, a=18.0,<br>
>> ><br>
>> > nat= 26, ntyp= 2,<br>
>> ><br>
>> > ecutwfc = 30d0,<br>
>> ><br>
>> > nbnd = 100,<br>
>> ><br>
>> > /<br>
>> ><br>
>> > &electrons<br>
>> ><br>
>> > conv_thr = 1.0e-9,<br>
>> ><br>
>> > mixing_beta = 0.7,<br>
>> ><br>
>> > mixing_mode = 'plain',<br>
>> ><br>
>> > diagonalization = 'cg'<br>
>> ><br>
>> > /<br>
>> ><br>
>> > &IONS<br>
>> ><br>
>> > /<br>
>> ><br>
>> ><br>
>> ><br>
>> > ATOMIC_SPECIES<br>
>> ><br>
>> > C 12.0107 C.pz-vbc.UPF<br>
>> ><br>
>> > H 1.007825035 H.pz-vbc.UPF<br>
>> ><br>
>> ><br>
>> ><br>
>> > ATOMIC_POSITIONS { angstrom }<br>
>> ><br>
>> > C 8.891700e+00 8.891700e+00 8.891700e+00<br>
>> ><br>
>> > C 9.783400e+00 9.783400e+00 8.000000e+00<br>
>> ><br>
>> > C 9.783400e+00 8.000000e+00 9.783400e+00<br>
>> ><br>
>> > C 8.000000e+00 9.783400e+00 9.783400e+00<br>
>> ><br>
>> > C 8.891700e+00 1.067510e+01 1.067510e+01<br>
>> ><br>
>> > C 1.067510e+01 1.067510e+01 8.891700e+00<br>
>> ><br>
>> > C 1.067510e+01 8.891700e+00 1.067510e+01<br>
>> ><br>
>> > C 9.783400e+00 1.156680e+01 9.783400e+00<br>
>> ><br>
>> > C 9.783400e+00 9.783400e+00 1.156680e+01<br>
>> ><br>
>> > C 1.156680e+01 9.783400e+00 9.783400e+00<br>
>> ><br>
>> > H 8.391700e+00 8.391700e+00 8.391700e+00<br>
>> ><br>
>> > H 7.500000e+00 1.028340e+01 9.283400e+00<br>
>> ><br>
>> > H 7.500000e+00 9.283400e+00 1.028340e+01<br>
>> ><br>
>> > H 9.283400e+00 1.028340e+01 7.500000e+00<br>
>> ><br>
>> > H 1.028340e+01 9.283400e+00 7.500000e+00<br>
>> ><br>
>> > H 9.283400e+00 7.500000e+00 1.028340e+01<br>
>> ><br>
>> > H 1.028340e+01 7.500000e+00 9.283400e+00<br>
>> ><br>
>> > H 9.283400e+00 1.206680e+01 9.283400e+00<br>
>> ><br>
>> > H 1.206680e+01 9.283400e+00 9.283400e+00<br>
>> ><br>
>> > H 9.283400e+00 9.283400e+00 1.206680e+01<br>
>> ><br>
>> > H 8.391700e+00 1.117510e+01 1.117510e+01<br>
>> ><br>
>> > H 1.117510e+01 1.117510e+01 8.391700e+00<br>
>> ><br>
>> > H 1.117510e+01 8.391700e+00 1.117510e+01<br>
>> ><br>
>> > H 1.028340e+01 1.206680e+01 1.028340e+01<br>
>> ><br>
>> > H 1.028340e+01 1.028340e+01 1.206680e+01<br>
>> ><br>
>> > H 1.206680e+01 1.028340e+01 1.028340e+01<br>
>> ><br>
>> ><br>
>> ><br>
>> ><br>
>> ><br>
>> > CELL_PARAMETERS {cubic}<br>
>> ><br>
>> > 1.00 0.00 0.00<br>
>> ><br>
>> > 0.00 1.00 0.00<br>
>> ><br>
>> > 0.00 0.00 1.00<br>
>> ><br>
>> ><br>
>> ><br>
>> > K_POINTS {gamma} {automatic}<br>
>> ><br>
>> > 1 1 1 0 0 0<br>
>> ><br>
>> ><br>
>> ><br>
>> ><br>
>> ><br>
>> > The program is run with<br>
>> ><br>
>> ><br>
>> ><br>
>> > mpirun -np 32 /path_xxx/pw.x<br>
>> ><br>
>> ><br>
>> ><br>
>> > Final coordinates: The first two rows for ecutwfc=30 for two runs with<br>
>> identical input are:<br>
>> ><br>
>> > ATOMIC_POSITIONS (angstrom)<br>
>> > C 8.898432121 8.898432121 8.898432121<br>
>> > C 9.783306562 9.783306562 8.019670107<br>
>> ><br>
>> > ATOMIC_POSITIONS (angstrom)<br>
>> > C 8.898432121 8.898432121 8.898432121<br>
>> > C 9.783306562 9.783306562 8.019670109<br>
>> ><br>
>> ><br>
>> > Final coordinates: The first two rows for ecutwfc=60 for two runs with<br>
>> identical input are:<br>
>> ><br>
>> > ATOMIC_POSITIONS (angstrom)<br>
>> > C 8.904988579 8.904988579 8.904988579<br>
>> > C 9.783426086 9.783426086 8.031809869<br>
>> ><br>
>> > ATOMIC_POSITIONS (angstrom)<br>
>> > C 8.904962246 8.904962246 8.904962246<br>
>> > C 9.783425401 9.783425401 8.031847251<br>
>> ><br>
>> > --<br>
>> > --<br>
>> ><br>
>> > Dr. Pablo García Risueño<br>
>> ><br>
>> > Institut für Physikalische Chemie, Universität Hamburg, Grindelallee<br>
>> 117, 20146 Hamburg<br>
>> ><br>
>> > Tel. +49 040 42 83 84 82 7<br>
>> ><br>
>> > ______________________________<wbr>_________________<br>
>> > Pw_forum mailing list<br>
>> > <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
>> > <a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/<wbr>listinfo/pw_forum</a><br>
>><br>
>><br>
>> ______________________________<wbr>_________________<br>
>> Pw_forum mailing list<br>
>> <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
>> <a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/<wbr>listinfo/pw_forum</a><br>
>><br>
><br>
><br>
><br>
> --<br>
> --<br>
><br>
> Dr. Pablo García Risueño<br>
><br>
> Institut für Physikalische Chemie, Universität Hamburg, Grindelallee 117,<br>
> 20146 Hamburg<br>
><br>
> Tel. <a href="tel:%2B49%20040%2042%2083%2084%2082%207" value="+4940428384827">+49 040 42 83 84 82 7</a><br>
<br>
<br>
<br>
______________________________<wbr>_________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" rel="noreferrer" target="_blank">http://pwscf.org/mailman/<wbr>listinfo/pw_forum</a></div></div></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">--<br><br>Dr. Pablo García Risueño<br><br>Institut für Physikalische Chemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg<br><br>Tel. +49 040 42 83 84 82 7</div></div></div></div></div></div>
</div></div>