<html><body><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt; color: #000000"><div>Hi Marco.<br></div><div><br></div><div>If I correctly understood, if you want to relax *only* some of yours atoms, you should impose some constrains in the <span class="card">ATOMIC_POSITIONS</span><br></div><div><br></div><div><br></div><div>http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm140629872010784</div><div><br></div><div>see <br></div><div><br></div><div>if_pos(1), if_pos(2), if_pos(3) INTEGER<br>Default: 1<br><br> component i of the force for this atom is multiplied by if_pos(i),<br> which must be either 0 or 1. Used to keep selected atoms and/or<br> selected components fixed in MD dynamics or<br> structural optimization run.<br><br> With crystal_sg atomic coordinates the constraints are copied in all equivalent<br> atoms. </div><div><br></div><div><br></div><div>Example:</div><div><br></div><div>ATOMIC_POSITIONS (ang)</div><div>Si 0.25 0.25 0.25 0 0 0 --> this will not move<br></div><div>Si 0.0 0.0 0.0 1 1 1 --> this will move<br></div><div><br></div><div><span name="x"></span><table class="mceItemTable" xmlns="urn:zimbraAccount"><tbody><tr><td><img alt="Université Paris-Sud" src="https://zimbra.u-psud.fr/public/z_logo_signature.png" style="border: 0pt none;width:120px;height:107px;background:url(data:image/png;base64,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"></td><td valign="top"><div><span style="font-size: 10pt"><b>Federico IORI</b></span></div><div><span style="font-size: 10pt">Marie Curie Fellow<br>Laboratoire de Physique des Solides<br>Bâtiment 510 - Rue André Rivière<br>91400 Orsay</span></div></td></tr></tbody></table><div><br data-mce-bogus="1"></div><span name="x"></span><br></div><hr id="zwchr"><div style="color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>De: </b>"Marco Di Gennaro" <marco.digennaro@unibas.ch><br><b>Para: </b>"pw forum" <pw_forum@pwscf.org><br><b>Enviados: </b>Miércoles, 24 de Mayo 2017 17:45:45<br><b>Asunto: </b>[Pw_forum] Relax Linear chain with constraint<br><div><br></div>
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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Dear PW users,<br>
<br>
I would like to relax my system while keeping some geometry constraints.<br>
<br>
Specifically, I have a linear chain composed of N atoms (say A,B,C).<br>
I want to know if it is possible to relax the distance among atoms only (so AB, BC and CA)<br>
while making sure that the system stays linear after the relaxation.<br>
<div><br>
Following the PW doc: <a href="http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node11.html" target="_blank">
http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node11.html</a><br>
I have tried with <tt>calculation='relax'</tt> and add namelist &IONS,<br>
but it looks like there is no relaxation at all.<br>
<br>
Thank you,<br>
<b>Marco Di Gennaro</b><span data-mce-style="color: #808080;" style="color: #808080;">,</span> <span data-mce-style="color: #808080;" style="color: #808080;">Dr.</span><br>
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