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<body class='hmmessage'><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" size="2" style="line-height: normal;"><span style="line-height: 19px;">-------------------------------------------------</span></font></h5><div><font color="#333333" face="verdana, tahoma" size="2" 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 size="2" 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 size="2" 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">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></body>
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