<div dir="ltr"><div class="gmail_default" style="font-family:'comic sans ms',sans-serif">I am a ware of what you are trying to do. The maximum number of atoms I dealt with was 64 atoms ( almost one third of your number) and I did it using the supercell direct method. On the other hand Gamma point is not enough.</div>
<div class="gmail_default" style="font-family:'comic sans ms',sans-serif"><br></div><div class="gmail_default" style="font-family:'comic sans ms',sans-serif">Thank you</div></div><div class="gmail_extra"><br clear="all">
<div><div dir="ltr">__________________________________<br><div>Iyad Al-Qasir, PhD</div><div>Assistant Professor</div><div><br></div><div>Department of Nuclear Engineering</div><div>University of Sharjah</div><div>Sharjah, UAE</div>
</div></div>
<br><br><div class="gmail_quote">On Sat, Dec 14, 2013 at 1:35 PM, Alex Granov <span dir="ltr"><<a href="mailto:alex.granov@outlook.com" target="_blank">alex.granov@outlook.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div dir="ltr"><pre><br></pre><pre>Dear I<span style="font-family:Calibri,sans-serif;font-size:12pt">yad</span></pre><pre><span style="font-family:Calibri,sans-serif;font-size:12pt"><br></span></pre><pre><span style="font-family:Calibri,sans-serif;font-size:12pt">The main matter is that it is almost impossible or quite expensive to calculate </span><i style="font-family:Calibri,sans-serif;font-size:12pt">entire phonon dispersion for a very large system that has about 160 atoms. </i><span style="font-family:Calibri,sans-serif;font-size:12pt">So I would like to know whether it is possible to calculate Thermodynamic properties by QHA avoiding such expensive step or do it only at the Gamma point. </span></pre>
<pre><span style="font-family:Calibri,sans-serif;font-size:12pt"><br></span></pre><pre><div style="font-family:Calibri,sans-serif;white-space:normal;line-height:21px;color:rgb(68,68,68);font-size:15px"><h5 style="font-size:15px;font-weight:normal;padding:0px;border:0px">
<font color="#333333" face="verdana, tahoma" style="line-height:normal"><span style="line-height:19px">-------------------------------------------------</span></font></h5><div><font color="#333333" face="verdana, tahoma" style="line-height:normal"><span style="line-height:19px">Alex Granov</span></font></div>
<h5 style="font-size:15px;font-weight:normal;padding:0px;border:0px"><font color="#333333" face="verdana, tahoma" style="line-height:normal"><span style="line-height:19px"><font style="line-height:normal">Московский физико-технический институт </font><font size="1" style="line-height:normal">(</font></span></font><span style="line-height:1.5;color:rgb(51,51,51);font-family:verdana,tahoma"><font size="1" style="line-height:normal">MIPT)</font></span></h5>
</div><div style="font-family:Calibri,sans-serif;white-space:normal;line-height:21px;color:rgb(68,68,68);font-size:15px"><h5 style="line-height:1.5;font-size:15px;font-weight:normal;padding:0px;border:0px;font-family:verdana,tahoma;color:rgb(51,51,51)">
<font style="line-height:normal">Moscow, Russia</font></h5></div></pre><pre><br></pre><pre>Hi Alex,
Thermodynamical quantities depend strongly on low energy phonons ( mainly
the acoustic phonons, or the low energy part of the phonon density of
states; the Debye part). And to less extent on the high energy modes.
It also depends on how much precise you want to go in your calculations.
The more q-vectors you use in your calculations the better convergence of
quantities of interests.
I think the best thing to do is to sample for once the phonon density of
states using a fine mesh of q-vectors, and then to use it to calculate all
your quantities for all temperatures of interests.
Kindest Regards,
__________________________________
Iyad Al-Qasir, PhD
Assistant Professor
Department of Nuclear Engineering
University of Sharjah
Sharjah, UAE
On Sat, Dec 14, 2013 at 3:04 AM, Alex Granov <<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">alex.granov at outlook.com</a>>wrote:
><i> Hi
</i>><i>
</i>><i> As I understand from Phonon and QHA examples calculation of entire phonon
</i>><i> dispersion is necessary to calculate and prepare fc file then
</i>><i> Thermodynamic properties like Gibbs energy. I wonder if it is possible to
</i>><i> avoid calculating entire phonon dispersion for a very large system say 160
</i>><i> atoms to calculate its Gibbs energy or not. I appreciate any help in
</i>><i> advance.
</i>><i>
</i>><i>
</i>><i> -------------------------------------------------
</i>><i> Alex Granov
</i>><i> Московский физико-технический институт (MIPT)
</i>><i> Moscow, Russia
</i>></pre><br><div style="line-height:21px;color:rgb(68,68,68);font-size:15px"><h5 style="font-size:15px;font-weight:normal;padding:0px;border:0px"><br></h5></div> </div></div>
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