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    <div class="moz-cite-prefix">Dear Ashkan Shekaari,<br>
         there is no general rule. it depends on how localized the
      augmentation charges are.<br>
         you should determine this by yourself and do not rely on other
      people suggestions.<br>
      <br>
         how to determine ecutwfc and ecutrho ?<br>
      <br>
         it's a 2-step procedure:<br>
         <br>
       1) Run a convergence test assuming the default ecutrho=4*ecutwfc
      value: that is just specify ecutwfc in the input and leave
      unspecified the ecutrho option. Converge the total energy and
      monitor stress and forces as well to make sure you get the
      convergence you want.<br>
      <br>
          This step tells you what is the ecutwfc and ecutrho=4*ecutwfc
      for which the variational freedom of wavefuctions AND the
      numerical accuracy of augmentation-charge integration are BOTH
      sufficient. The latter is usually the harder to get so you should
      take this value of ecutrho as the one needed for your system.<br>
      <br>
        2) Keeping fixed this value of ecutrho you can now test the
      convergence w.r.t. ecutwfc and see if you can reduce it without
      compromising the convergence of total energy, stress and forces.
      This tells you the value of ecutwfc you should use in your system.<br>
      <br>
        HTH<br>
      <br>
      stefano<br>
      <br>
      <br>
      stefano<br>
      <br>
       <br>
      <br>
      <br>
      <br>
      stefano<br>
      <br>
      On 03/06/2016 09:51, ashkan shekaari wrote:<br>
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      <div dir="ltr">Dear experts,
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        <div>Is it necessary to take the kinetic energy cut-off for the
          charge density and the potential 8-12 times larger than the
          energy cut-off for the wave functions for the case of 2D-MoS2?</div>
        <div><br>
        </div>
        <div>Doesn't a less value of about 4 times larger than the
          energy cut-off for the wave functions work?</div>
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                                      <div><b>--</b></div>
                                      <div><i style="font-size:12.8px">Best,</i></div>
                                      <div><i>Ashkan Shekaari</i></div>
                                      <div><i>Plasma Physics Research
                                          Center</i></div>
                                      <div><i style="font-size:12.8px"><span
                                            style="font-size:12.8px">Science
                                            and Research Branch</span></i></div>
                                      <div><i>I A U, <span
                                            style="font-size:12.8px">14778-93855
                                            Tehran, Iran.</span></i></div>
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