<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Sep 13, 2008, at 2:20 PM, vega wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> <div id="MailContainerBody" style="PADDING-RIGHT: 10px; PADDING-LEFT: 10px; PADDING-TOP: 15px; WORD-WRAP: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space" bgcolor="#ffffff" leftmargin="0" topmargin="0" canvastabstop="true" name="Compose message area"> <div><font face="Arial" size="2">Dear sir,</font></div> <div><font face="Arial" size="2"></font> </div> <div><font face="Arial" size="2">Thank you for your responding.</font></div> <div><font face="Arial" size="2"></font> </div> <div><font face="Arial" size="2">Could you tell me what is the most important thing to judge whether the <font face="Times New Roman" size="3">accuracy of a numerical calculation is enough.</font></font></div> <div>The energy? force? atomic coordinates? or any other things?</div></div></blockquote><div><br></div>It depends on what you are interested in, of course. What you are interested in (geometry, energy, other properties ...) is what you should look at ... for instance, it is known that obtaining well converged values for the dielectric constant may require k-point meshes way finer than required for a plain energy calculation. Here as well as in many other circumstances, the correct answer is not one that the beginner may like to hear: "it depends" ...</div><div><br></div><div>life is beatiful and hard. if it were not as hard, it would not be as beautiful</div><div><br></div><div>cheers - SB</div><div><br><blockquote type="cite"><div id="MailContainerBody" style="PADDING-RIGHT: 10px; PADDING-LEFT: 10px; PADDING-TOP: 15px; WORD-WRAP: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space" bgcolor="#ffffff" leftmargin="0" topmargin="0" canvastabstop="true" name="Compose message area"> <div> </div> <div><font face="Arial" size="2">vega</font></div> <div><font face="Arial" size="2"></font> </div> <div><font face="Arial" size="2">=================================================================================<br>Vega Lew (weijia liu)<br>PH.D Candidate in Chemical Engineering<br>State Key Laboratory of Materials-oriented Chemical Engineering<br>College of Chemistry and Chemical Engineering<br>Nanjing University of Technology, 210009, Nanjing, Jiangsu, China</font></div> <div style="FONT: 10pt Tahoma"> <div><br></div> <div style="BACKGROUND: #f5f5f5"> <div style="font-color: black"><b>From:</b> <a title="baroni@sissa.it" href="mailto:baroni@sissa.it">Stefano Baroni</a> </div> <div><b>Sent:</b> Saturday, September 13, 2008 6:04 PM</div> <div><b>To:</b> <a title="pw_forum@pwscf.org" href="mailto:pw_forum@pwscf.org">PWSCF Forum</a> </div> <div><b>Subject:</b> Re: [Pw_forum] Fw: relax is too slow</div></div></div> <div><br></div>the same way as you would choose any other parameter controlling the accuracy of a numerical calculation. try a value; try a few others corresponding to increasing accuracy, and stop when you see that the increase in the accuracy is not worth the extra workload. never forget to use common sense (whenever it is available). <div><br></div> <div>SB</div> <div><br> <div> <div>On Sep 12, 2008, at 11:36 AM, vega wrote:</div><br class="Apple-interchange-newline"> <blockquote type="cite"> <div>Dear sir<br> <blockquote type="cite">vega wrote:<br></blockquote> <blockquote type="cite"><br></blockquote> <blockquote type="cite"> <blockquote type="cite">As far as I tested, the energy would be within 1% for large supercells,<br></blockquote></blockquote> <blockquote type="cite"> <blockquote type="cite">but the coordinates of several atoms may differ 200%.<br></blockquote></blockquote> <blockquote type="cite"><br></blockquote> <blockquote type="cite">doesn't make sense<br></blockquote><br>could you tell me more about how to choose the k point mesh?<br><br>vega<br>=================================================================================<br>Vega Lew (weijia liu)<br>PH.D Candidate in Chemical Engineering<br>State Key Laboratory of Materials-oriented Chemical Engineering<br>College of Chemistry and Chemical Engineering<br>Nanjing University of Technology, 210009, Nanjing, Jiangsu, China<br><br>--------------------------------------------------<br>From: "Paolo Giannozzi" <<a href="mailto:giannozz@democritos.it">giannozz@democritos.it</a>><br>Sent: Friday, September 12, 2008 5:27 PM<br>To: "PWSCF Forum" <<a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>Subject: Re: [Pw_forum] Fw: relax is too slow<br><br><br> <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>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum">http://www.democritos.it/mailman/listinfo/pw_forum</a><br></div></blockquote></div><br> <div apple-content-edited="true"><span class="Apple-style-span" style="WORD-SPACING: 0px; FONT: 14px Helvetica; TEXT-TRANSFORM: none; COLOR: rgb(0,0,0); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BORDER-COLLAPSE: separate; orphans: 2; widows: 2; -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="WORD-SPACING: 0px; FONT: 14px Helvetica; TEXT-TRANSFORM: none; COLOR: rgb(0,0,0); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BORDER-COLLAPSE: separate; orphans: 2; widows: 2; -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="WORD-SPACING: 0px; FONT: 14px Helvetica; TEXT-TRANSFORM: none; COLOR: rgb(0,0,0); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BORDER-COLLAPSE: separate; orphans: 2; widows: 2; -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="WORD-SPACING: 0px; FONT: 14px Helvetica; TEXT-TRANSFORM: none; COLOR: rgb(0,0,0); TEXT-INDENT: 0px; WHITE-SPACE: normal; LETTER-SPACING: normal; BORDER-COLLAPSE: separate; orphans: 2; widows: 2; -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: 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">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">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> <br class="webkit-block-placeholder"></div><hr><div><br class="webkit-block-placeholder"></div>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>http://www.democritos.it/mailman/listinfo/pw_forum<br></div> _______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>http://www.democritos.it/mailman/listinfo/pw_forum<br></blockquote></div><br></body></html>