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<p>Dear all, </p>
<p>I encounter an issue I did not expect and I would like to know why it happens and how I am suppose to handle it. I'm running an SCF calculation of a gapped system (occupations = 'fixed'). If I include a large number of empty bands, these are the energies in Gamma:</p>
<p class="p1"><span class="s1"><span class="Apple-converted-space"> </span>-4.8200<span class="Apple-converted-space"> </span>-4.3169<span class="Apple-converted-space"> </span>-0.9586<span class="Apple-converted-space"> </span>-0.5478<span class="Apple-converted-space"> </span>-0.5196<span class="Apple-converted-space"> </span>-0.4977<span class="Apple-converted-space"> </span>-0.0537 <span class="Apple-converted-space"> </span>0.0095 </span><span class="s1">with occupations </span><span class="s1"><span class="Apple-converted-space"> </span>1.0000 <span class="Apple-converted-space"> </span>1.0000 <span class="Apple-converted-space"> </span>0.0000 <span class="Apple-converted-space"> </span>0.0000 <span class="Apple-converted-space"> </span>0.0000 <span class="Apple-converted-space"> </span>0.0000 <span class="Apple-converted-space"> </span>0.0000 <span class="Apple-converted-space"> </span>0.0000</span></p>
<p class="p1"><span class="s1">Instead, if I include only one empty band the result is </span></p>
<p class="p1"><span class="s1">-4.8200<span class="Apple-converted-space"> </span>-4.3169<span class="Apple-converted-space"> </span>-0.5477 </span><span class="Apple-converted-space" style="font-size: 10pt;">with occupations </span><span class="Apple-converted-space" style="font-size: 10pt;"> </span><span style="font-size: 10pt;">1.0000 </span><span class="Apple-converted-space" style="font-size: 10pt;"> </span><span style="font-size: 10pt;">1.0000 </span><span class="Apple-converted-space" style="font-size: 10pt;"> </span><span style="font-size: 10pt;">0.0000</span></p>
<p class="p1"><span class="s1">It's like in if the latter case I was missing the state at -0.9586 eV. How it happens ? </span></p>
<p class="p1"><span class="s1">I'm rising this issue because I'm checking the gapwidth of a series of similar systems. I actually thought that it was safe to run simple SCF calculations with 1 empty state, but I realise that results are possibly wrong. Shall I mandatorily rely on NSCF calculations or I'm making a mistake somewhere ? </span></p>
<p>Best regards</p>
<div id="signature">-- <br />
<div class="pre" style="margin: 0; padding: 0; font-family: monospace">Dr. Lorenzo Sponza<br />Chargé de Recherche au CNRS<br />Laboratoire d'étude de microstructures (LEM), CNRS-ONERA<br />29 Avenue de la division Leclerc, 92322 Châtillon<br />Tel: +33146734464</div>
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