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<div>I have calculated the cell parameters and band-gap energy
by GGA and GGA+U for CaMnO3 materiels (orthorhombic structure
). I tried two U values, one from the literature (U1=4.18 eV)
and I have calculated the other one by the first principal
method with the quantum espresso package (U2=5.7722 eV ). The
band-gap energies whose I have calculated by GGA, GGA+U1 and
GGA+U2 are 0.71eV, 0.80 eV and 0.88 eV respectively. However,
these values are very small in comparison to the experimental
result Eg=3.07 eV. <br>
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<p>Hello, I would proceed in two directions:</p>
<p>1. examine the band structure with projwfc, in order to determine
which is the character of the states close to the gap (es. Mn d,
or Oxygen O...). The applying a +U to those states can open the
gap.</p>
<p>2. add an arbitrary but not absurd U to all species and see if I
can manage to open the gap in this way or if it is absolutely
impossible</p>
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<p>cheers<br>
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<div><br>
U2 was calculated by hp.x code in QE (version 6.5) package
with 2*1*2 and 2*2*2 kpoints. In addition, 2*1*2 and 2*2*2
gave the same U2 value .<br>
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<div>you can find my input files below</div>
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<div><span style="color:rgb(136,136,136)">--</span><br
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<div><span style="font-family:tahoma,sans-serif"><font
size="2" color="#444444"><b>Best regards,</b></font></span><br>
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<div>-------------------------------------</div>
<div><b>Mohammed Lamhani,</b> Ph.D. </div>
<div><i>LS3M Laboratory, Polydisciplinary Faculty of
Khouribga, Sultan Moulay Slimane University of Beni
Mellal, Morocco.</i></div>
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