<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><BR><DIV><DIV>On Jul 27, 2007, at 12:13 AM, Tengfei Luo wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2">Dear all:</FONT></DIV> <DIV><FONT face="Arial" size="2">I'm new to PWscf. I tried the first example which includes the total energy calculation of Si. The result I got from this example was: </FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">! total energy = -15.84452726 Ry</FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">I believe this is for the total energy of the two Si atoms system. However, from the reference data here:</FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2"><A href="http://physics.nist.gov/PhysRefData/DFTdata/Tables/14Si.html">http://physics.nist.gov/PhysRefData/DFTdata/Tables/14Si.html</A></FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">The total energy is -288.198397 a.u.. The caluclated data is very different from this. Is this because of using of pesudopotential? <BR></FONT></DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV>YES</DIV><DIV><BR><BLOCKQUOTE type="cite"><DIV><FONT face="Arial" size="2">How can I get the real totoal energy?<BR></FONT></DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV>1) Do an all-electron calculation</DIV><DIV>2) If you want something aproximate, you may want to add to the PWscf total energy twice the difference berween the all-electron energy of an isolated atom and its energy calculated with the _same_ pseudopotential that you use for the solid-state calculation. Best if the difference is calculated between the all-electron atomic energy obtained by a real-space code and the pseudopotential atomic energy calculated with plane waves (you can do that with PWscf, with some care, if you wish). The reason is PW calculations introduve extra numerical errors due to the limited basis set.</DIV><DIV><BR><BLOCKQUOTE type="cite"><DIV><FONT face="Arial" size="2"> </FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> <FONT class="Apple-style-span" face="Arial" size="3"><SPAN class="Apple-style-span" style="font-size: 11px;">I would appreciate any help!</SPAN></FONT></DIV></BLOCKQUOTE></DIV><DIV><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">Thank you!</FONT></DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV><DIV><DIV><BR class="khtml-block-placeholder"></DIV>you are most welcome</DIV><DIV><BR class="khtml-block-placeholder"></DIV><BLOCKQUOTE type="cite"><DIV> </DIV> <DIV><FONT face="Arial" size="2">Tengfei</FONT></DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV>please, do not forget to add your affiliation to your signature</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Stefano</DIV><BR><BR><DIV> <SPAN class="Apple-style-span" style="border-collapse: separate; 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"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; ">Stefano Baroni - SISSA</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><FONT class="Apple-style-span" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "> </SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><FONT class="Apple-style-span" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;"><SPAN class="Apple-style-span" style="font-size: 12px; 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"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; ">Please, if possible, don't</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><FONT class="Apple-style-span" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "> </SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><FONT class="Apple-style-span" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;"><SPAN class="Apple-style-span" style="font-size: 12px; 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"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; ">Why? See:</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><FONT class="Apple-style-span" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;"><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "><SPAN class="Apple-style-span" style="font-size: 12px; "> </SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT><A href="http://www.gnu.org/philosophy/no-word-attachments.html"><FONT class="Apple-style-span" color="#0023E9" size="3"><SPAN class="Apple-style-span" style="font-size: 12px;; color: rgb(0, 35, 233); -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><SPAN class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; ">http://www.gnu.org/philosophy/no-word-attachments.html</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT></A></DIV><DIV><BR class="khtml-block-placeholder"></DIV><BR class="Apple-interchange-newline"></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN> </DIV><BR></BODY></HTML>