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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have a questions about relax and vc-relax using pw.x. I tried to use them to optimize the geometry of graphite, and the atoms can barely move even though I move them manually I can get lower energy. I’m not sure why.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For example, I take 7 layers of ABAB stacked grapheme, fix the bottom 6 layers using the geometry parameters of graphite(000 thing), and relax the top layer. Geometry is defined as ibrav=14, celldm(1)=xx, celldm(3)=22.0(should be big enough),
nosym=.true. Default bfgs optimization parameters are taken. The calculation usually takes a few iterations and stops, with the top layer moved by only 0.0002 A. But if I manually pull the top layer away by 0.7A, the energy lowers by 0.0005Ry. It also didn’t
help by increasing trust_radius_max and trust_radius_ini to 3.0 and 1.0. Is this behavior expected? How do I make it converge to a real minimum?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I can run test calculation example02/al001.mm.in just fine.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thank you very much,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Rain<o:p></o:p></p>
<p class="MsoNormal">Department of Chemistry<o:p></o:p></p>
<p class="MsoNormal">University of North Dakota<o:p></o:p></p>
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