<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Jun 19, 2008, at 4:17 PM, <a href="mailto:stewart@cnf.cornell.edu">stewart@cnf.cornell.edu</a> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Fig 2 (D. A. Stewart, New. J. Phys. 10 043025 (2008)). Of course, the <br>difference you get between ASR results and direct calculations will depend <br>strongly on how well relaxed your structure is. </div></blockquote><div><br></div>hmmm: this may well be the case, but if this is so, it must be for a nontrivial reason (which, if true, would qualify the "of course" as slightly misplaced).</div><div><br></div><div>the total force acting on any isolated system is of course zero, even though the system is not at equilibrium ("not well relaxed"). in particular, this total force is invariant ("invariantly zero!") with respect to a homogeneous translation of the system. therefore, the system must have a zero mode (actually three of them: one for each cartesian coordinate), irrespective on how well (or how bad) the internal degrees of freedom have been optimized.</div><div><br></div><div>is this wrong?</div><div><br></div><div>SB</div><div><br><blockquote type="cite"><div><br><br><a href="http://dx.doi.org/10.1088/1367-2630/10/4/043025">http://dx.doi.org/10.1088/1367-2630/10/4/043025</a> <br><br>Best regards, <br><br>Derek <br><br><br>Paolo Giannozzi writes: <br><br><blockquote type="cite"><a href="mailto:xwzhang@uestc.edu.cn">xwzhang@uestc.edu.cn</a> wrote: <br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><blockquote type="cite">are there any problem that the slope of the phonon around Gamma is <br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">incorrect, because ASR cure the problem of k=0, but what about other <br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">points near it? <br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">for phonons at k/=0, the error due to ASR violation seems to be<br></blockquote><blockquote type="cite">usually negligible. I never tried to make calculations with<br></blockquote><blockquote type="cite">very small q, though. <br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Paolo<br></blockquote><blockquote type="cite">-- <br></blockquote><blockquote type="cite">Paolo Giannozzi, Democritos and University of Udine, Italy<br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">Pw_forum mailing list<br></blockquote><blockquote type="cite"><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br></blockquote><blockquote type="cite"><a href="http://www.democritos.it/mailman/listinfo/pw_forum">http://www.democritos.it/mailman/listinfo/pw_forum</a> <br></blockquote><blockquote type="cite"><br></blockquote><br><br><br>################################<br>Derek Stewart, Ph. D.<br>Scientific Computation Associate<br><a href="http://www.people.cornell.edu/pages/das248/">http://www.people.cornell.edu/pages/das248/</a><br>250 Duffield Hall<br>Cornell Nanoscale Facility (CNF)<br>Ithaca, NY 14853<br>stewart (at) cnf.cornell.edu<br>(607) 255-2856<br>_______________________________________________<br>Pw_forum mailing list<br>Pw_forum@pwscf.org<br>http://www.democritos.it/mailman/listinfo/pw_forum<br></div></blockquote></div><br><div> <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; "><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; ">[+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; "><span class="Apple-style-span" style="font-size: 14px; "><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; "><br></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; ">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></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><br></body></html>