<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi Mohaddesh. I do not understand why you say that the calculated frequency (which, I assume you define as 2 * Delta E / u^2 ???) does not converge as u->0. According to your plot, it does, and to a reasonable value. The finite slope of your plot around u=0 seems to me nothing but a manifestation of cubic anharmonicity ... What's wrong in this? SB<div><br><div><div>On Aug 1, 2011, at 3:01 PM, mohaddeseh abbasnejad wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><br>Dear users,<br clear="all">
<div style="text-align:justify;direction:ltr" dir="ltr"><br>I have
plotted the harmonic frequency (obtained within the frozen phonon
approach) of Diamond as a function of atomic displacements (small
displacements in the [1 1 1] direction, u(1)=±(u,u,u) and
u(2)=±(-u,-u,-u) are the displacements of two atoms in the basis). I
expect to see a range of displacements that tend to the similar
frequency, but there is no convergence in the plot. Also, the
displacements with the same amplitude but different in sign, do not tend
to the same frequency, which is not what I expect, too. The plot is attached. <br>I was wondering
if anyone could help me to find the source of error. I should expect the
mentioned symmetry, right? Why there is no convergence?</div>
<div style="text-align:justify;direction:ltr" dir="ltr"> </div>
<div style="text-align:justify;direction:ltr" dir="ltr">Thanks in advance.</div>
<div style="text-align:justify;direction:ltr" dir="ltr"> </div>
<div style="text-align:justify;direction:ltr" dir="ltr">Yours,</div>
<div style="text-align:justify;direction:ltr" dir="ltr">Mohaddeseh</div>---------------------------------------------------------<br><br>Mohaddeseh Abbasnejad, <br>Room No. 323, Department of Physics, <br>University of Tehran, North Karegar Ave.,<br>
Tehran, P.O. Box: 14395-547- IRAN <br>E-Mail: <a href="mailto:m.abbasnejad@gmail.com" target="_blank">m.abbasnejad@gmail.com</a><br>
Website: <a href="http://physics.ut.ac.ir/" target="_blank">http://physics.ut.ac.ir</a><br><br>---------------------------------------------------------<br><br>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -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; font-size: medium; "><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">---</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><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-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="http://stefano.baroni.me/">http://stefano.baroni.me</a> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><br style="font-size: 12px; "></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><span class="Apple-style-span" style="font-size: 14px; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 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-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 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-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><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-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><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><div><font class="Apple-style-span" color="#0023E9" size="3"><br></font></div></span><br class="Apple-interchange-newline">
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