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    <div class="moz-cite-prefix">Dear Lucian <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">I would first try setting </div>
    <div class="moz-cite-prefix">pot_extrapolation='none' in the
      electrons namelist. If the problem is caused by the extrapolation
      this should make it go away. <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">for the calculation with vacuum I would
      also set <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">cell_dofree='ibrav+2Dxy' <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">hope this can solve your problem <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">best regards <br>
    </div>
    <div class="moz-cite-prefix">Pietro <br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix"><br>
    </div>
    <div class="moz-cite-prefix">On 7/25/22 21:45, Lucian D. Filip
      wrote:<br>
    </div>
    <blockquote type="cite" cite="mid:df3d43f8-54a3-b87a-b2bd-a590a7ed082e@infim.ro">
      
      Hello all,
      <p>I have stumbled on a problem that is very frustrating and
        cannot figure out what is happening. I am trying to do a
        vc-relax of a rather large structure 115 atoms. It constits of
        3-SrRuO3/7-PbTiO3/3-SrTiO3/7-PbTiO3/3-SrRuO3. The numbers in
        front of the materials represent the number of unit cells of
        each material. The structure is 1x1x23. I have tried both with
        vacuum on either side (about 15 A because if I add more then the
        FFT limit is reached and I get that error) and in super cell
        configuration (i.e. no vacuum) but the same thing happens:</p>
      <p>The calculation starts  and the first scf step converges in 240
        iterations. I know it is a large number but the structure is
        also large and I have seen that this is quite common for these
        cases. I may be wrong thou... The starting charge is  951.8694,
        renormalised to     952.0000. All is good and the first step
        converges. Then in the second step starts the weird part:</p>
      <p>extrapolated charge  991.00311, renormalised to  952.00000</p>
      <p>Then it tries to perform the first scf step and the calculation
        dies with the: <br>
      </p>
      <p>Error in c_bands(1):</p>
      <p>too many bands are not converged</p>
      <p>I do not understand what is happening because I have
        succesfully relaxed slightly smaller but similar structures:
        3-SrRuO3/7-PbTiO3/3-SrTiO3/3-SrRuO3 and
        3-SrRuO3/7-PbTiO3/3-SrRuO3. These two I relaxed with 15A of
        vacuum on either side.</p>
      <p><br>
      </p>
      <p>I am using ultrasoft PBE PPs. <br>
      </p>
      <p>Here is the input I used:</p>
      <p><br>
      </p>
      <p>&control<br>
         calculation         = 'vc-relax'<br>
         restart_mode        = 'from_scratch'<br>
         prefix              = '10Fd-3i-10Fd-slab'<br>
         disk_io             = 'low'<br>
         tstress             = .true.<br>
         tprnfor             = .true.<br>
         etot_conv_thr       = 1.e-4<br>
         forc_conv_thr       = 1.e-4<br>
         verbosity           = 'high'<br>
         pseudo_dir          = '../pp/pbe-US/'<br>
         outdir              = '10Fd-3i-10Fd-slab'<br>
         nstep               = 600<br>
        /<br>
        <br>
        &system<br>
         ibrav               = 6<br>
         celldm(1)           = 7.37937998548<br>
         celldm(3)           = 28.8910838525<br>
         nat                 = 115<br>
         ntyp                = 5<br>
         ecutwfc             = 60.<br>
         ecutrho             = 480.<br>
         occupations         = 'smearing'<br>
         degauss             = 0.01<br>
         smearing            = 'gaussian'<br>
        /<br>
        <br>
        &electrons<br>
         diagonalization     = 'david'<br>
         mixing_beta         = 0.1<br>
         mixing_mode         = 'local-TF'<br>
         conv_thr            = 1.e-8<br>
         scf_must_converge   = .false.<br>
         electron_maxstep    = 400<br>
        /<br>
        <br>
        &ions<br>
         ion_dynamics        = 'bfgs'<br>
        /<br>
        <br>
        &cell<br>
         cell_dynamics       = 'bfgs'<br>
        /<br>
        <br>
        ATOMIC_SPECIES<br>
         Pb    1              Pb.pbe-dn-rrkjus_psl.0.2.2.UPF<br>
         Ti    1              Ti.pbe-spn-rrkjus_psl.1.0.0.UPF<br>
         O     1               O.pbe-n-rrkjus_psl.0.1.UPF<br>
         Sr    1              Sr.pbe-spn-rrkjus_psl.1.0.0.UPF<br>
         Ru    1              Ru.pbe-n-van.UPF<br>
        <br>
        ATOMIC_POSITIONS {angstrom}<br>
        Sr  0.00000000000000    0.00000000000000    0.00000000000000<br>
        O   1.95250000000000    1.95250000000000    0.00000000000000<br>
        Ru  1.95250000000000    1.95250000000000    1.95250000000000<br>
        O   0.00000000000000    1.95250000000000    1.95250000000000<br>
        O   1.95250000000000    0.00000000000000    1.95250000000000<br>
        Sr  0.00000000000000    0.00000000000000    3.90500000000000<br>
        O   1.95250000000000    1.95250000000000    3.90500000000000<br>
        Ru  1.95250000000000    1.95250000000000    5.85750000000000<br>
        O   0.00000000000000    1.95250000000000    5.85750000000000<br>
        O   1.95250000000000    0.00000000000000    5.85750000000000<br>
        Sr  0.00000000000000    0.00000000000000    7.81000000000000<br>
        O   1.95250000000000    1.95250000000000    7.81000000000000<br>
        Ru  1.95250000000000    1.95250000000000    9.76250000000000<br>
        O   0.00000000000000    1.95250000000000    9.76250000000000<br>
        O   1.95250000000000    0.00000000000000    9.76250000000000<br>
        Pb  0.00000000000000    0.00000000000000    11.7202344916000<br>
        O   1.95250000000000    1.95250000000000    12.1688551695000<br>
        Ti  1.95250000000000    1.95250000000000    13.9438177707000<br>
        O   0.00000000000000    1.95250000000000    14.2579079188000<br>
        O   1.95250000000000    0.00000000000000    14.2579079188000<br>
        Pb  0.00000000000000    0.00000000000000    15.8398546661000<br>
        O   1.95250000000000    1.95250000000000    16.2884753441000<br>
        Ti  1.95250000000000    1.95250000000000    18.0634379452000<br>
        O   0.00000000000000    1.95250000000000    18.3775280934000<br>
        O   1.95250000000000    0.00000000000000    18.3775280934000<br>
        Pb  0.00000000000000    0.00000000000000    19.9594748407000<br>
        O   1.95250000000000    1.95250000000000    20.4080955187000<br>
        Ti  1.95250000000000    1.95250000000000    22.1830581198000<br>
        O   0.00000000000000    1.95250000000000    22.4971482679000<br>
        O   1.95250000000000    0.00000000000000    22.4971482679000<br>
        Pb  0.00000000000000    0.00000000000000    24.0790950152000<br>
        O   1.95250000000000    1.95250000000000    24.5277156932000<br>
        Ti  1.95250000000000    1.95250000000000    26.3026782943000<br>
        O   0.00000000000000    1.95250000000000    26.6167684425000<br>
        O   1.95250000000000    0.00000000000000    26.6167684425000<br>
        Pb  0.00000000000000    0.00000000000000    28.1987151898000<br>
        O   1.95250000000000    1.95250000000000    28.6473358678000<br>
        Ti  1.95250000000000    1.95250000000000    30.4222984689000<br>
        O   0.00000000000000    1.95250000000000    30.7363886171000<br>
        O   1.95250000000000    0.00000000000000    30.7363886171000<br>
        Pb  0.00000000000000    0.00000000000000    32.3183353644000<br>
        O   1.95250000000000    1.95250000000000    32.7669560423000<br>
        Ti  1.95250000000000    1.95250000000000    34.5419186435000<br>
        O   0.00000000000000    1.95250000000000    34.8560087916000<br>
        O   1.95250000000000    0.00000000000000    34.8560087916000<br>
        Pb  0.00000000000000    0.00000000000000    36.4379555389000<br>
        O   1.95250000000000    1.95250000000000    36.8865762169000<br>
        Ti  1.95250000000000    1.95250000000000    38.6615388180000<br>
        O   0.00000000000000    1.95250000000000    38.9756289662000<br>
        O   1.95250000000000    0.00000000000000    38.9756289662000<br>
        Sr  0.00000000000000    0.00000000000000    40.5523412219000<br>
        O   1.95250000000000    1.95250000000000    40.5523412219000<br>
        Ti  1.95250000000000    1.95250000000000    42.5048412219000<br>
        O   0.00000000000000    1.95250000000000    42.5048412219000<br>
        O   1.95250000000000    0.00000000000000    42.5048412219000<br>
        Sr  0.00000000000000    0.00000000000000    44.4573412219000<br>
        O   1.95250000000000    1.95250000000000    44.4573412219000<br>
        Ti  1.95250000000000    1.95250000000000    46.4098412219000<br>
        O   0.00000000000000    1.95250000000000    46.4098412219000<br>
        O   1.95250000000000    0.00000000000000    46.4098412219000<br>
        Sr  0.00000000000000    0.00000000000000    48.3623412219000<br>
        O   1.95250000000000    1.95250000000000    48.3623412219000<br>
        Ti  1.95250000000000    1.95250000000000    50.3148412219000<br>
        O   0.00000000000000    1.95250000000000    50.3148412219000<br>
        O   1.95250000000000    0.00000000000000    50.3148412219000<br>
        Pb  0.00000000000000    0.00000000000000    52.2725757135000<br>
        O   1.95250000000000    1.95250000000000    52.7211963915000<br>
        Ti  1.95250000000000    1.95250000000000    54.4961589926000<br>
        O   0.00000000000000    1.95250000000000    54.8102491407000<br>
        O   1.95250000000000    0.00000000000000    54.8102491407000<br>
        Pb  0.00000000000000    0.00000000000000    56.3921958880000<br>
        O   1.95250000000000    1.95250000000000    56.8408165660000<br>
        Ti  1.95250000000000    1.95250000000000    58.6157791671000<br>
        O   0.00000000000000    1.95250000000000    58.9298693153000<br>
        O   1.95250000000000    0.00000000000000    58.9298693153000<br>
        Pb  0.00000000000000    0.00000000000000    60.5118160626000<br>
        O   1.95250000000000    1.95250000000000    60.9604367406000<br>
        Ti  1.95250000000000    1.95250000000000    62.7353993417000<br>
        O   0.00000000000000    1.95250000000000    63.0494894899000<br>
        O   1.95250000000000    0.00000000000000    63.0494894899000<br>
        Pb  0.00000000000000    0.00000000000000    64.6314362372000<br>
        O   1.95250000000000    1.95250000000000    65.0800569151000<br>
        Ti  1.95250000000000    1.95250000000000    66.8550195163000<br>
        O   0.00000000000000    1.95250000000000    67.1691096644000<br>
        O   1.95250000000000    0.00000000000000    67.1691096644000<br>
        Pb  0.00000000000000    0.00000000000000    68.7510564117000<br>
        O   1.95250000000000    1.95250000000000    69.1996770897000<br>
        Ti  1.95250000000000    1.95250000000000    70.9746396908000<br>
        O   0.00000000000000    1.95250000000000    71.2887298390000<br>
        O   1.95250000000000    0.00000000000000    71.2887298390000<br>
        Pb  0.00000000000000    0.00000000000000    72.8706765863000<br>
        O   1.95250000000000    1.95250000000000    73.3192972643000<br>
        Ti  1.95250000000000    1.95250000000000    75.0942598654000<br>
        O   0.00000000000000    1.95250000000000    75.4083500135000<br>
        O   1.95250000000000    0.00000000000000    75.4083500135000<br>
        Pb  0.00000000000000    0.00000000000000    76.9902967608000<br>
        O   1.95250000000000    1.95250000000000    77.4389174388000<br>
        Ti  1.95250000000000    1.95250000000000    79.2138800399000<br>
        O   0.00000000000000    1.95250000000000    79.5279701881000<br>
        O   1.95250000000000    0.00000000000000    79.5279701881000<br>
        Sr  0.00000000000000    0.00000000000000    81.1046824438000<br>
        O   1.95250000000000    1.95250000000000    81.1046824438000<br>
        Ru  1.95250000000000    1.95250000000000    83.0571824438000<br>
        O   0.00000000000000    1.95250000000000    83.0571824438000<br>
        O   1.95250000000000    0.00000000000000    83.0571824438000<br>
        Sr  0.00000000000000    0.00000000000000    85.0096824438000<br>
        O   1.95250000000000    1.95250000000000    85.0096824438000<br>
        Ru  1.95250000000000    1.95250000000000    86.9621824438000<br>
        O   0.00000000000000    1.95250000000000    86.9621824438000<br>
        O   1.95250000000000    0.00000000000000    86.9621824438000<br>
        Sr  0.00000000000000    0.00000000000000    88.9146824438000<br>
        O   1.95250000000000    1.95250000000000    88.9146824438000<br>
        Ru  1.95250000000000    1.95250000000000    90.8671824438000<br>
        O   0.00000000000000    1.95250000000000    90.8671824438000<br>
        O   1.95250000000000    0.00000000000000    90.8671824438000<br>
        <br>
        K_POINTS {automatic}<br>
         3 3 1 0 0 0<br>
        <br>
      </p>
      <p>Regards,</p>
      <p><br>
      </p>
      <p>Lucian<br>
      </p>
      <div class="moz-signature">-- <br>
        <b>Dr. Lucian Dragos Filip</b><br>
        National Institute of Materials Physics<br>
        Atomistilor str. 405A, PO Box MG. 7<br>
        Magurele, 077125<br>
        Bucharest, Romania<br>
        E-mail: <url><a class="moz-txt-link-abbreviated
            moz-txt-link-freetext" href="mailto:lucian.filip@infim.ro" moz-do-not-send="true">lucian.filip@infim.ro</a></url><br>
        Website: <url><a class="moz-txt-link-freetext" href="https://lucianfilip.wordpress.com/" moz-do-not-send="true">https://lucianfilip.wordpress.com/</a></url><br>
      </div>
      <br>
      <fieldset class="moz-mime-attachment-header"></fieldset>
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    </blockquote>
    <p><br>
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