<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top" style="font: inherit;"><div>Dear Prof. Stefano</div>
<div>I have taken the your suggestions for the first two of my questions.</div>
<div>Regarding the third one, </div>
<div>' 3. to do a 'vc-relax', what displacement pattern I better follow?' What I mean here is that in my in put file for the 'vc-relax' in what way I better displace(disturb) the atoms? </div>
<div><em>I have</em> already done a phonon calculation for my system unrelaxed(the atoms in their ideal positions) and found negative phonon frequencies at gamma, M, and R.</div>
<div> <br>--- On <b>Sat, 1/31/09, Stefano Baroni <i><<a href="mailto:baroni@sissa.it">baroni@sissa.it</a>></i></b> wrote:<br></div>
<blockquote style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: rgb(16,16,255) 2px solid">From: Stefano Baroni <<a href="mailto:baroni@sissa.it">baroni@sissa.it</a>><br>Subject: Re: [Pw_forum] How/where to get DISPLACEMENT PATTERN<br>To: <a href="mailto:bayleyegn_aq@yahoo.com">bayleyegn_aq@yahoo.com</a>, "PWSCF Forum" <<a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>Date: Saturday, January 31, 2009, 4:53 AM<br><br>
<div id="yiv1597941611">Dear Bayleyegn Akane:
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<div>I am graduate student at Addis Ababa Univerity-Ethiopia. Currently I am working on my thesis using the Quantum-Espresso package.</div></div></td></tr></tbody></table></blockquote>
<div><br></div>welcom on board!</div>
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<div> <em> I am trying to do phonon calculation with my system relaxed.. There</em> are three points that I want to be clear about for now:</div>
<div>1. when can I say that a system is fully relaxed?</div></div></td></tr></tbody></table></blockquote>
<div><br></div>when the forces acting on atoms and the acroscopic stress are "small enough". How small is "small"? As small as getting it even smaller would not change the quantity you want to calculate (phonon frequencies, in you case) to within your target accuracy. What the target accuracy has to be, only YOU can say ...</div>
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<div>2. should I do simple 'relax' prior to a 'vc-relax'?</div></div></td></tr></tbody></table></blockquote>
<div><br></div>it depends how far your volume/ cell shape is from their equilibrium state. all in all, it is probably safer do some experimentation by yourself and gain some confidence on what you are doing, than relying on the advice of other people ...</div>
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<div>3. to do a 'vc-relax', what displacement pattern I better follow?</div></div></td></tr></tbody></table></blockquote>
<div><br></div>sorry: I do not quite undererstand the question ...<br></div>
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<div style="MARGIN: 0px">take care - Stefano B</div>
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<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">---</span></font></div>
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">Stefano Baroni - SISSA</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">&</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">DEMOCRITOS National Simulation Center - Trieste</span></font></div>
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"><a href="http://www.sissa.it/~baroni" target="_blank" rel="nofollow">http://www.sissa.it/~baroni</a> / [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div>
<div style="MIN-HEIGHT: 14px; MARGIN: 0px; FONT: 12px Helvetica"><br style="FONT-SIZE: 12px"></div>
<div style="MIN-HEIGHT: 14px; MARGIN: 0px; FONT: 12px Helvetica"><span class="Apple-style-span" style="FONT-SIZE: 14px">
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget</span></font></div>
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"><br></span></font></div></span></div>
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">Please, if possible, don't</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">send me MS Word or PowerPoint attachments</span></font></div>
<div style="MARGIN: 0px"><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px">Why? See:</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"> </span></font><font class="Apple-style-span" color="#0023e9" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"><a href="http://www.gnu.org/philosophy/no-word-attachments.html" target="_blank" rel="nofollow">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div>
<div><font class="Apple-style-span" color="#0023e9" size="3"><span class="Apple-style-span" style="FONT-SIZE: 12px"><br class="webkit-block-placeholder"></span></font></div></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div><br></div></div></blockquote></td></tr></tbody></table><br>
<br><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">---</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Stefano Baroni - SISSA</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">&</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">DEMOCRITOS National Simulation Center - Trieste</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="http://www.sissa.it/~baroni">http://www.sissa.it/~baroni</a> / [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><br style="font-size: 12px; "></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><span class="Apple-style-span" style="font-size: 14px; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br></span></font></div></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Please, if possible, don't</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">send me MS Word or PowerPoint attachments</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Why? See:</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" color="#0023E9" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="http://www.gnu.org/philosophy/no-word-attachments.html">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div><div><font class="Apple-style-span" color="#0023E9" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"> </div><br></body></html>