<p dir="ltr">Dear Naren,<br>
Increase ecut. Use more intense kpoint mesh.</p>
<div class="gmail_extra"><br><div class="gmail_quote">On Apr 21, 2017 4:50 PM, "Giuseppe Mattioli" <<a href="mailto:giuseppe.mattioli@ism.cnr.it">giuseppe.mattioli@ism.cnr.it</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
Dear Naren<br>
Your calculation is very expensive, and calculations of 0D objects in a plane-wave/PBC framework are often prone to convergence issues. This said, you<br>
can try to<br>
<br>
1) perform a simple calculation of the PbSe unit cell with the same pseudopotentials. Are there similar convergence problems? You are using hgh that<br>
are norm-conserving pseudopotentials (NCPP) and they could require a richer pw basis set. I would not be surprised if, after proper convergence tests<br>
performed on the unit cell, you ended up with ecutwfc=70~80 Ry. There is no need to specify ecutrho, anyway. It is fixed to a default ecutwfc*4 value<br>
in the case of NCPP.<br>
<br>
2) lower mixing_beta, even down to very small values such as 0.05~0.01. Sometimes it helps to reach convergence (slowly but steady).<br>
<br>
It is impossible to say more without looking at you cluster, but if it is simply cut out from the bulk along low-index directions (e.g., a cube) you<br>
have to deal with a mess of surface dangling bonds that want to play nasty charge displacements between occupied and unoccupied electronic levels,<br>
even inducing a metallic character in your cluster. People used to saturate such dangling bonds with pseudo-H atoms (H atoms having formal charge<br>
lower or higher than 1.0, depending on the formal valence of the saturated atom). If you don't want to saturate the surface you must keep into account<br>
the possibility that the cluster surface reconstruct, and you should anticipate reconstruction trends by lplacing the atoms nearer to the expected<br>
final positions. It could be a very difficult task, look at the instructive story of the Si 7x7 reconstruction in this movie!<br>
<br>
<a href="https://www.youtube.com/watch?v=BXdC0NhAMBY" rel="noreferrer" target="_blank">https://www.youtube.com/watch?<wbr>v=BXdC0NhAMBY</a><br>
<br>
HTH<br>
Giuseppe<br>
<br>
On Friday, April 21, 2017 04:06:06 AM Narendranath Ghosh wrote:<br>
> Dear all!<br>
><br>
><br>
><br>
> I am currently trying to optimizing a Pb180Se180 cluster using QE.<br>
><br>
> But after 83 iterations it didn’t get converged.<br>
><br>
> *Input *<br>
><br>
> calculation='relax',<br>
><br>
> outdir='/staging/op/NAREN_USC/<wbr>PbSe_360_FINAL_based_Pb68Se68/<wbr>OUTPUT',<br>
><br>
> prefix='PbSe-360',<br>
><br>
> pseudo_dir='/staging/op/NAREN_<wbr>USC/PbSe_360_FINAL_based_<wbr>Pb68Se68/pseudo',<br>
><br>
> verbosity='low',<br>
><br>
> /<br>
><br>
><br>
><br>
> &SYSTEM<br>
><br>
> ibrav=0,<br>
><br>
> celldm(1)=90.7068539791d0,<br>
><br>
> nat=360,<br>
><br>
> ntyp=2,<br>
><br>
> ecutwfc=30.0d0,<br>
><br>
> ecutrho=120.0d0,<br>
><br>
> input_dft='PBE',<br>
><br>
> occupations='smearing',<br>
><br>
> smearing='gaussian',<br>
><br>
> degauss=0.002000d0,<br>
><br>
> /<br>
><br>
> &ELECTRONS<br>
><br>
> diagonalization='david',<br>
><br>
> mixing_mode='plain',<br>
><br>
> mixing_beta=0.700d0,<br>
><br>
> /<br>
><br>
> &IONS<br>
><br>
> /<br>
><br>
> ATOMIC_SPECIES<br>
><br>
> Pb 207.200000d0 Pb.pbe-hgh.UPF<br>
><br>
> Se 78.960000d0 Se.pbe-hgh.UPF<br>
><br>
><br>
><br>
> ATOMIC_POSITIONS {alat}<br>
><br>
> Pb 0.4831100000d0 0.4740500000d0 0.4999300000d0<br>
><br>
> Se 0.5190800000d0 0.5278700000d0 0.5981100000d0<br>
><br>
> Se 0.5901900000d0 0.4712600000d0 0.2154800000d0<br>
><br>
> …………………………<wbr>…………………………<wbr>………….<br>
><br>
> K_POINTS {gamma}<br>
><br>
><br>
><br>
> CELL_PARAMETERS {alat}<br>
><br>
> 1.000000000000d0 0.000000000000d0 0.000000000000d0<br>
><br>
> 0.000000000000d0 1.000000000000d0 0.000000000000d0<br>
><br>
> 0.000000000000d0 0.000000000000d0 1.000000000000d0<br>
><br>
><br>
><br>
><br>
><br>
> *Output*<br>
><br>
> iteration # 81 ecut= 30.00 Ry beta=0.70<br>
><br>
> Davidson diagonalization with overlap<br>
><br>
> WARNING: 9 eigenvalues not converged in regterg<br>
><br>
> ethr = 4.62E-04, avg # of iterations = 21.0<br>
><br>
><br>
><br>
> total cpu time spent up to now is 92680.3 secs<br>
><br>
><br>
><br>
> total energy = 2098.58547221 Ry<br>
><br>
> Harris-Foulkes estimate = -16225.87153481 Ry<br>
><br>
> estimated scf accuracy < 209398.02191142 Ry<br>
><br>
><br>
><br>
> iteration # 82 ecut= 30.00 Ry beta=0.70<br>
><br>
> Davidson diagonalization with overlap<br>
><br>
> WARNING: 5 eigenvalues not converged in regterg<br>
><br>
> c_bands: 5 eigenvalues not converged<br>
><br>
> ethr = 4.62E-04, avg # of iterations = 20.0<br>
><br>
><br>
><br>
> total cpu time spent up to now is 95793.4 secs<br>
><br>
><br>
><br>
> total energy = 1914.32044477 Ry<br>
><br>
> Harris-Foulkes estimate = -18801.41916562 Ry<br>
><br>
> estimated scf accuracy < 243341.55571758 Ry<br>
><br>
><br>
><br>
> iteration # 83 ecut= 30.00 Ry beta=0.70<br>
><br>
> Davidson diagonalization with overlap<br>
><br>
> WARNING: 138 eigenvalues not converged in regterg<br>
><br>
> ethr = 4.62E-04, avg # of iterations = 27.0<br>
><br>
><br>
><br>
> total cpu time spent up to now is 99442.6 secs<br>
><br>
><br>
><br>
> total energy = 1659.36438352 Ry<br>
><br>
> Harris-Foulkes estimate = -15989.48139862 Ry<br>
><br>
> estimated scf accuracy < 138246.99363207 Ry<br>
><br>
><br>
><br>
> Any comment to help me getting started is very much appreciated!<br>
><br>
><br>
><br>
> Best regards,<br>
><br>
> Naren<br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
> *Dr. Narendra Nath Ghosh*<br>
><br>
> *Research Associate*<br>
><br>
> *University of Gour Banga*<br>
><br>
> *Department of Chemistry*<br>
><br>
> *Malda-732102*<br>
><br>
> *India*<br>
><br>
> *Phone: +919126667601*<br>
<br>
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<br>
Giuseppe Mattioli<br>
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
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E-mail: <<a href="mailto:giuseppe.mattioli@ism.cnr.it">giuseppe.mattioli@ism.cnr.it</a>><br>
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ResearcherID: F-6308-2012<br>
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</blockquote></div></div>