<DIV>Dear Stefano,</DIV>  <DIV>    I'm sorry. I did not explain my question clearly.</DIV>  <DIV>    I found a softening transverse acaustic mode at X (TA(X)) point on the brillouin zone boundary in a NaCl structure.  Since  the first high-pressure phase that the experiment observed is CsCl structure,  could the soft mode be considered as  the driven force of the transition from NaCl to CsCl? </DIV>  <DIV>    If it could not, may i give an intermediate state between the NaCl and CsCl phase if I can get a energy favored structure in terns of the softening mode in the NaCl structure? It is a monoclinic phase, obtained by moving the atoms along the displacements (order parameters) corresponding to the softening mode.</DIV>  <DIV> </DIV>  <DIV> Thank you very much for any advice. </DIV> 
 <DIV> </DIV>  <DIV> Best regards.</DIV>  <DIV> </DIV>  <DIV><B><I>Stefano Baroni <baroni@sissa.it></I></B> Ð´µÀ£º</DIV>  <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>  <DIV>  <DIV>On Jun 15, 2007, at 3:20 AM, li yan wrote:</DIV><BR class=Apple-interchange-newline>  <BLOCKQUOTE type="cite">  <DIV>Dear Stefano</DIV>  <DIV>     I'm so sorry and giving my delayed thanks to you, </DIV>  <DIV>     I am not sure if i can continue the discussion of my previous question. I have read the papers you suggested. And the authors proposed that the softening mode coupled with the lattice strain can induced a second or a slightly first order pahse transition. But I stil have doubts in the displacive instabilitis. </DIV>  <DIV>   The character of the  transition from NaCl to CsCl is thougt to be?first order in experiment. May I cosider this  transition to be induced by the lattice instability if I found the
 softening mode in the  NaCl phase at the pressure which is consitent with the experiment??lt;/DIV></DIV></BLOCKQUOTE>  <DIV><BR class=khtml-block-placeholder></DIV>which normal-mode displacement would bring the NaCl structure to CsCl? what would be the order parameter of the transition?</DIV>  <DIV><BR class=khtml-block-placeholder></DIV>  <DIV>S.</DIV><BR>  <DIV><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; border-spacing: 0px 0px; orphans: 2; widows: 2; khtml-text-decorations-in-effect: none; apple-text-size-adjust: auto"><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; border-spacing: 0px 0px; orphans: 2; widows: 2; khtml-text-decorations-in-effect:
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 style="MARGIN: 0px"><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">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"><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"><SPAN class=Apple-style-span
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 Trieste</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT></DIV>  <DIV style="MARGIN: 0px"><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">[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT></DIV>  <DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px"><BR class=khtml-block-placeholder></SPAN></FONT></DIV>  <DIV style="MARGIN: 0px"><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">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"><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">send me MS Word or PowerPoint attachments</SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></FONT></DIV>  <DIV style="MARGIN: 0px"><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">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="FONT-SIZE: 12px; COLOR: rgb(0,35,233); khtml-text-decorations-in-effect: underline"><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="FONT-SIZE: 12px; COLOR: rgb(0,35,233); khtml-text-decorations-in-effect: underline"><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="FONT-SIZE: 12px; COLOR: rgb(0,35,233); khtml-text-decorations-in-effect: underline"><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="FONT-SIZE: 12px; COLOR: rgb(0,35,233); khtml-text-decorations-in-effect: underline"><SPAN class=Apple-style-span style="FONT-SIZE: 12px; COLOR: rgb(0,35,233); 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></BLOCKQUOTE><BR><p>
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