<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Aug 1, 2011, at 4:56 PM, mohaddeseh abbasnejad wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><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"> </span></div></blockquote><div><br></div>what range? why should it?</div><div><br><blockquote type="cite"><div><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></blockquote><div><br></div>yes, by definition</div><div><br><blockquote type="cite"><div>
</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. </div></blockquote><div><br></div>why should you?</div><div><br><blockquote type="cite"><div>Shouldn't the plot have
symmetry vs. the vertical axis?</div></blockquote><div><br></div>why?</div><div><br></div><div>please, try you best to answer my questions, and I will make my best to let you understand</div><div><br></div><div>SB</div><div><br><blockquote type="cite">
<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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<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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