<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /></head><body style='font-size: 10pt; font-family: Verdana,Geneva,sans-serif'>
<p>El 06-08-2019 09:28, MARIA CATERINA CEVALLOS BRENES escribió:</p>
<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0"><!-- html ignored --><!-- head ignored --><!-- meta ignored -->
<p>Dear QE community:</p>
<p>I am having several errors when trying to get the relaxed structure of polyacetylene. I am supposed to get 1.36 and 1.43 as the dimer bond lengths (for C=C and C-C respectively).</p>
<p>I am using vc-relax method, just allowing z lattice parameter (along the chain) to change.</p>
<p>Here is my input file:</p>
<p class="p1"><span class="s1"><span>&</span>control</span></p>
<p class="p1"><span class="s1">calculation = 'vc-relax',</span></p>
<p class="p1"><span class="s1">prefix = 'pa',</span></p>
<p class="p1"><span class="s1">verbosity = 'low',</span></p>
<p class="p1"><span class="s1">pseudo_dir = '/home/ccevallos/pslibrary.1.0.0/pbe/PSEUDOPOTENTIALS',</span></p>
<p class="p1"><span class="s1">outdir = './tmp',</span></p>
<p class="p1"><span class="s1">wf_collect=.true.</span></p>
<p class="p1"><span class="s1">/</span></p>
<p class="p2"> </p>
<p class="p1"><span class="s1">&SYSTEM</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>ibrav = 0,</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>nat=4,</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>ntyp=2,</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>ecutwfc=200.00,</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>occupations = 'fixed',</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>input_DFT='PBE',</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>nbnd= 12,</span></p>
<p class="p1"><span class="s1">/</span></p>
<p class="p2"> </p>
<p class="p1"><span class="s1">&ELECTRONS</span></p>
<p class="p1"><span class="s1">/</span></p>
<p class="p2"> </p>
<p class="p1"><span class="s1">&ions</span></p>
<p class="p1"><span class="s1">/</span></p>
<p class="p2"> </p>
<p class="p1"><span class="s1">&cell</span></p>
<p class="p1"><span class="s1">cell_dofree='z'</span></p>
<p class="p1"><span class="s1">/</span></p>
<p class="p1"><span class="s1">ATOMIC_SPECIES</span></p>
<p class="p1"><span class="s1">C 12.011 C.pbe-n-rrkjus_psl.1.0.0.UPF</span></p>
<p class="p1"><span class="s1">H 1.00784 H.pbe-rrkjus_psl.1.0.0.UPF</span></p>
<p> </p>
<p class="p1"><span class="s1">CELL_PARAMETERS {angstrom}</span></p>
<p class="p1"><span class="s1">5.000000000000000 <span class="Apple-converted-space"> </span>0.000000000000000 <span class="Apple-converted-space"> </span>0.000000000000000</span></p>
<p class="p1"><span class="s1">0.000000000000000 <span class="Apple-converted-space"> </span>5.000000000000000 <span class="Apple-converted-space"> </span>0.000000000000000</span></p>
<p class="p1"><span class="s1">0.000000000000000 <span class="Apple-converted-space"> </span>0.000000000000000 <span class="Apple-converted-space"> </span>2.4</span></p>
<p class="p1"><span class="s1">ATOMIC_POSITIONS {angstrom}</span></p>
<p class="p1"><span class="s1">C 2.8 0 0</span></p>
<p class="p1"><span class="s1">C 2.1 0 1.16</span></p>
<p class="p1"><span class="s1">H 3.89 0 0</span></p>
<p class="p1"><span class="s1">H 3.19 0 1.16</span></p>
<p class="p1"> </p>
<p class="p1"><span class="s1">K_POINTS automatic</span></p>
<p class="p1"><span class="s1">2 2 25 1 1 1</span></p>
<p> </p>
<p>However I am getting the following error:</p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>Error in routine cdiaghg (30):</span></p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>S matrix not positive definite</span></p>
<p class="p1"> </p>
<p class="p1">What am I doing wrong? I also tried using a larger supercell, with 4 Carbon atoms, and it gives the same error, but you can see the bond length getting closer to 1.39 for al C-C bond lengths. In the latter case, why am I not observing the Peierls distortion? </p>
<p class="p1">Thank you very much in advance!</p>
<p class="p1">Best regards,</p>
<p class="p1">Caterina Cevallos.</p>
<p class="p1">QCLab. University of Costa Rica</p>
<div> </div>
<!-- html ignored --><br />
<div class="pre" style="margin: 0; padding: 0; font-family: monospace">_______________________________________________<br /> Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu/quantum-espresso">www.max-centre.eu/quantum-espresso</a>)<br /> users mailing list <a href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a><br /> <a href="https://lists.quantum-espresso.org/mailman/listinfo/users">https://lists.quantum-espresso.org/mailman/listinfo/users</a></div>
</blockquote>
<p>There are two errors with the input file:</p>
<p>Last atomic position should be:</p>
<p><span>H 1.01 0 1.16</span> </p>
<p>and nbnd=10 </p>
<p>However, I'm still not getting the dimerization expected. </p>
<div> </div>
</body></html>