<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Dear Bertrand:<br>
<br>
1) The MSD is quadratic in time at the beginning if you start with
finite velocities. If you start with zero velocities the MSD will be
even slower (t**4 in principle). For a fluid, the asymptotic behavior
is linear in t, for a solid it converges to a finite value (which can
be connected to the Debye-Waller factor of x-ray intensities) in a time
scale comparable to the vibrational time scale, so not too slow. <br>
2) The MSD computed in cp.x are 3-D.<br>
3) MSD's are computed in subroutine "ions_displacement" which can be
found inside "ions_base.f90" in directory "Modules".<br>
<br>
Your simulation looks ok, except perhaps for the linear dependence in t
at the beginning, but the quadratic (or other) initial laws are
generally seen only in the first very few steps, 10-20 steps are more
than enough to spoil the ideal behavior typically. <br>
<br>
Sandro<br>
<br>
<br>
<blockquote cite="mid:967354.13531.qm@web26501.mail.ukl.yahoo.com"
type="cite">
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td
style="font-family: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; font-size: inherit; line-height: inherit; font-size-adjust: inherit; font-stretch: inherit; -x-system-font: none;"
valign="top"><br>
<br>
I am running CP dynamic with fixed temperature for a given solid
system, using cp.x. The microcanonical calculation went very well with
a conserved energy.Now the energy is still conserved. But my emphasis
is on the mean square displacement(MSD) of atoms. They are calculated
and plotted as a function of time.<br>
At the begining, the dependence seems to be linear at after, the MSD
seem to oscillate around certain values which can be taken as a mean
value after a sufficiently long time. My questions are:<br>
1) According to the litterature, the dependence at the beginning should
be quadratic and became linear after a long time. But for condensed
system as a solid it is, the MSD should saturate after a<span
style="font-weight: bold;"> very</span> long time. What is happening
for my case?<br>
2) The MSD computed with cp.x are tree dimensionnal. Please, confirm it
or not.<br>
3) In which file should I see how those MSD are computed?<br>
<br>
<br>
Thanks very much for your help<br>
<br>
<br>
***************************<br>
Bertrand SITAMTZE YOUMBI<br>
Laboratory of Material Sciences<br>
Department of Physics<br>
University of Yaounde I-Cameroon<br>
****************************<br>
<br>
</td>
</tr>
</tbody>
</table>
<br>
<pre wrap="">
<fieldset class="mimeAttachmentHeader"></fieldset>
_______________________________________________
Pw_forum mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a>
<a class="moz-txt-link-freetext" href="http://www.democritos.it/mailman/listinfo/pw_forum">http://www.democritos.it/mailman/listinfo/pw_forum</a>
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Sandro Scandolo, ICTP | <a class="moz-txt-link-freetext" href="http://www.ictp.it/~scandolo">http://www.ictp.it/~scandolo</a>
</pre>
</body>
</html>