<div>Dear Prof. Baroni</div>
<div> </div>
<div>Thanks for your reply.</div>
<div>I wonder shouldn't the plot show the same frequency for a range of displacements?<span dir="ltr" id=":1yb"> And the same freq. for the range to be the harmonic frequency? or the zero displacement limit, is the harmonic frequency?</span><br>
</div>
<div>And when I test the displacements with the same amplitude, but
different in sign (regarding the inward and outward atomic movements in
the basis) I do not get the same results. Shouldn't the plot have
symmetry vs. the vertical axis?</div>
<div> </div>
<div>Thank You again<br>Mohaddeseh<br></div><br><br><div class="gmail_quote">On Mon, Aug 1, 2011 at 6:33 PM, Stefano Baroni <span dir="ltr"><<a href="mailto:baroni@sissa.it">baroni@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div style="word-wrap:break-word">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><div></div><div class="h5"><div>On Aug 1, 2011, at 3:01 PM, mohaddeseh abbasnejad wrote:</div><br></div></div><blockquote type="cite"><div><div></div><div class="h5"><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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<font size="3"><span style="font-size:12px">Stefano Baroni - SISSA</span></font><font size="3"><span style="font-size:12px"> </span></font><font size="3"><span style="font-size:12px">&</span></font><font size="3"><span style="font-size:12px"> </span></font><font size="3"><span style="font-size:12px">DEMOCRITOS National Simulation Center - Trieste</span></font></div>
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<span style="font-size:14px"><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><font size="3"><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 size="3"><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 size="3"><span style="font-size:12px">Please, if possible, don't</span></font><font size="3"><span style="font-size:12px"> </span></font><font size="3"><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 size="3"><span style="font-size:12px">Why? See:</span></font><font size="3"><span style="font-size:12px"> </span></font><font color="#0023E9" size="3"><span style="font-size:12px"><a href="http://www.gnu.org/philosophy/no-word-attachments.html" target="_blank">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div>
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<br></blockquote></div><br><br clear="all"><br>-- <br>---------------------------------------------------------<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>Tel. No.: +98 21 6111 8634 & Fax No.: +98 21 8800 4781<br>Cellphone: +98 917 731 7514<br>E-Mail: <a href="mailto:m.abbasnejad@gmail.com" target="_blank">m.abbasnejad@gmail.com</a><br>
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