<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Just a small note to be fair to Keane EOS after recently posted examples:<div>As far as I know, Keane EOS is based on an assumption at high pressure.(B' is a monotonicly decreasing function of pressure, and reaches to a limiting value as pressure goes to infinity) Therefore it works best when both low pressure and high pressure input is supplied and intermediate pressure values are found (like when we interpolate between acoustic lab data and shock wave data) So the deviations are not weird when only 5% compression is considered. </div><div><div><div><div><div>cheers, </div><div>emine kucubenli, SISSA, Italy</div><div><br>--- On <b>Wed, 9/9/09, Tone Kokalj <i><tone.kokalj@ijs.si></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Tone Kokalj
<tone.kokalj@ijs.si><br>Subject: Re: [Pw_forum] using ev.x<br>To: "PWSCF Forum" <pw_forum@pwscf.org><br>Date: Wednesday, September 9, 2009, 2:02 PM<br><br><div class="plainMail"><br>Let me just add one more item about bulk modulus.<br><br>>From time to time I see the bulk modulus written with too many<br>significant digits, e.g. 179.3 GPa. Due to the fact that it is a second<br>derivative calculated numerically and due to a signal/noise that Stefano<br>mentioned, it is a sensitive quantity. E.g. adding a few additional data<br>point(s) (or expanding/shrinking the range) may easily change the last<br>two digits above. <br><br>Here is an example (silver-bulk) of how bulk modulus changes with the<br>number of data points (the range of scan is from -4% to +4%, and the<br>fits are performed for several subsets of so-obtained data points):<br><br><br>Bulk Modulus, B0 (in kbar units)::<br><br>
------------+------------+------------+------------+-----------<br> # points | MURNAGHAN | BIRCH O(1) | BIRCH O(2) | KEANE <br> ------------+------------+------------+------------+-----------<br> 15: 1--15 | 896 | 905 | 905 | 610 <br> 14: 1--14 | 898 | 905 | 904 | 755 <br> 13: 2--14 | 898 | 905 | 903 | 638 <br> 12: 2--13 | 900 | 904 | 903 |
748 <br> 11: 3--13 | 900 | 904 | 904 | 645 <br> 10: 3--12 | 901 | 904 | 905 | 599 <br> 9: 4--12 | 901 | 904 | 910 | 665 <br> 8: 4--11 | 906 | 907 | 909 | 602 <br> 7: 5--11 | 905 | 907 | 906 |
672 <br> ------------+------------+------------+------------+-----------<br><br>(the meaning of the first column is "number-of-points: first-point -- last-point")<br><br>To add to the Murnaghan vs Keane discussion, it is evident that the<br>Keane column above displays the largest fluctuations (and also <br>different result compared to others). <br><br>Regards, Tone<br><br><br>P.S.: for those interested: the above table was produced by the PWTK <br>(<a href="http://qe-forge.org/projects/pwtk/" target="_blank">http://qe-forge.org/projects/pwtk/</a>) which can calculate lattice<br>parameter and bulk modulus automatically. For more info see:<br><br>Tutorial:<br><a href="http://pwtk.qe-forge.org/tutorial.html" target="_blank">http://pwtk.qe-forge.org/tutorial.html</a><br><br>Examples:<br><a href="http://pwtk.qe-forge.org/documentation_tclPWTK2F32E20Examples.html"
target="_blank">http://pwtk.qe-forge.org/documentation_tclPWTK2F32E20Examples.html</a><br><br>-- <br>Anton Kokalj<br>J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia <br>(tel: +386-1-477-3523 // fax:+386-1-477-3822)<br><br>Please, if possible, avoid sending me Word or PowerPoint attachments.<br>See: <a href="http://www.gnu.org/philosophy/no-word-attachments.html" target="_blank">http://www.gnu.org/philosophy/no-word-attachments.html</a><br><br><br>_______________________________________________<br>Pw_forum mailing list<br><a ymailto="mailto:Pw_forum@pwscf.org" href="/mc/compose?to=Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br></div></blockquote></div></div></div></div></div></td></tr></table><br>