<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12pt"><div><span>Hi</span></div><div style="color: rgb(0, 0, 0); font-size: 16px; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida Grande', sans-serif; background-color: transparent; font-style: normal;"><span>I propose to fix only 3 or 4 first layers and permit another layers to be optimized. When you change the first layer's positions manually, you force the atoms to pass the potential barrier. I think the code's algorithms (such as another codes) can raise small value to the potential, and if the potential barrier is high, it can not change the atoms very high to pass it. It finds only local minimum around it.</span></div><div></div><div> </div><div>With the Best Regards</div><div><br><br></div><div> Reza Behjatmanesh-Ardakani<br> Associate Professor of Physical
Chemistry<br> Address:<br> Department of Chemistry,<br> School of Science,<br> Payame Noor University (PNU),<br> Ardakan,<br> Yazd,<br> Iran.<br> E-mails: <br> 1- reza_b_m_a@yahoo.com (preferred),<br> 2- behjatmanesh@pnu.ac.ir, <br> 3- reza.b.m.a@gmail.com.</div><div class="yahoo_quoted" style="display: block;"> <br> <br> <div style="font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida Grande', sans-serif; font-size: 12pt;"> <div style="font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida Grande', sans-serif; font-size: 12pt;"> <div dir="ltr"> <font size="2" face="Arial"> On Tuesday, December 10, 2013 4:13 AM, "Li, Run" <run.li@my.und.edu> wrote:<br> </font> </div> <div class="y_msg_container"><div id="yiv8249197064">
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<div class="yiv8249197064MsoNormal">Hello,</div>
<div class="yiv8249197064MsoNormal"> </div>
<div class="yiv8249197064MsoNormal">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.</div>
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<div class="yiv8249197064MsoNormal">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?</div>
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<div class="yiv8249197064MsoNormal">I can run test calculation example02/al001.mm.in just fine.</div>
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<div class="yiv8249197064MsoNormal">Thank you very much,</div>
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<div class="yiv8249197064MsoNormal">Rain</div>
<div class="yiv8249197064MsoNormal">Department of Chemistry</div>
<div class="yiv8249197064MsoNormal">University of North Dakota</div>
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