<div dir="ltr">Dear Prof. Paolo,<div><br></div><div>Thank you for boosting my thoughts in VCA implemented in Quantum Espresso. I'll conduct some tests of calculation.</div><div><br></div><div>Best regards!</div><div>Yue-Wen FANG<br>
<div class="gmail_extra"><br><div class="gmail_quote">2013/11/19 Paolo Giannozzi <span dir="ltr"><<a href="mailto:paolo.giannozzi@uniud.it" target="_blank">paolo.giannozzi@uniud.it</a>></span><br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div class="im">On Tue, 2013-11-19 at 23:16 +0800, Yue-Wen Fang wrote:<br>
<br>
> I still don't how to set it while using VCA. For example, in SrTiO3<br>
> bulk material, if I want to mix O with N(namely nitrogen dopping) ,<br>
> after getting a mixed PP's with virtual.x, the atomic weight of oxygen<br>
> in ATOMIC_SPECIES tag is hard to determine if I intend to do phonon<br>
> calculations.<br>
<br>
</div>VCA may (or may not) work for the electronic structure, but I<br>
doubt it will work for phonons, especially if the difference<br>
in mass is significant and especially for phonon branches that<br>
have significantly different energies in the case of pure atoms.<br>
You may assume that the mass of the virtual atom is equal to the<br>
weighted average of the two masses, with no warranty.<br>
Code "dynmat.x" allows to use the force constants (that do not<br>
depend upon masses) of the virtual crystal into a supercell of<br>
"real" atoms with different masses. Not sure it is suitable for<br>
your case, and not sure still works: it was written 20 or so<br>
years ago, used for phonons in GaAS/AlAs superlattices and<br>
GaAsAl alloys in which such "mass approximaton" works well:<br>
Phys. Rev. B 41, 3870 (1990), Phys. Rev. Lett. 65, 84 (1990).<br>
<span class=""><font color="#888888"><br>
P.<br>
</font></span><div class=""><div class="h5">> 2013/11/19 Paolo Giannozzi <<a href="mailto:paolo.giannozzi@uniud.it">paolo.giannozzi@uniud.it</a>><br>
> On Tue, 2013-11-19 at 08:52 +0800, Yue-Wen Fang wrote:<br>
><br>
> > In quantum espresso, what is determined by atomic weight?<br>
><br>
><br>
> molecular dynamics and dynamical matrices (phonons)<br>
><br>
> > In other words, why the atomic weight can be set freely by<br>
> users.<br>
><br>
> such possibility may be useful if you want to take into<br>
> account<br>
> isotopic effects, for instance<br>
><br>
> P.<br>
><br>
> > Thank you.<br>
> ><br>
> ><br>
> > 2013/11/18 Paolo Giannozzi <<a href="mailto:paolo.giannozzi@uniud.it">paolo.giannozzi@uniud.it</a>><br>
> > On Mon, 2013-11-18 at 19:03 +0800, Yue-Wen Fang<br>
> wrote:<br>
> ><br>
> > > Additionally, when using mixed PPs generated by<br>
> virtual.x,<br>
> > > how to determine the atomic weight?<br>
> ><br>
> ><br>
> > atomic weights are used only for molecular dynamics<br>
> > and phonon calculations. Unless you want to perform<br>
> > such calculations using VCA (likely not a good idea)<br>
> > you may choose whatever atomic weight you like<br>
> ><br>
> > P.<br>
> > --<br>
> > Paolo Giannozzi, Dept.<br>
> Chemistry&Physics&Environment,<br>
> > Univ. Udine, via delle Scienze 208, 33100 Udine,<br>
> Italy<br>
> > Phone +39-0432-558216, fax +39-0432-558222<br>
> ><br>
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> ><br>
> ><br>
> ><br>
> ><br>
> > --<br>
> ><br>
> ------------------------------------------------------------------------------------------------------------<br>
> > Yue-Wen FANG, PhD candidate<br>
> > Key Laboratory of Polar Materials and Devices, Ministry of<br>
> Education<br>
> > East China Normal University<br>
> ><br>
> ><br>
> ><br>
> ><br>
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><br>
> --<br>
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,<br>
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>
> Phone +39-0432-558216, fax +39-0432-558222<br>
><br>
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><br>
><br>
><br>
><br>
><br>
> --<br>
> ------------------------------------------------------------------------------------------------------------<br>
> Yue-Wen FANG, PhD candidate<br>
> Key Laboratory of Polar Materials and Devices, Ministry of Education<br>
> East China Normal University<br>
><br>
><br>
><br>
><br>
><br>
><br>
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<br>
--<br>
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,<br>
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>
Phone +39-0432-558216, fax +39-0432-558222<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr">------------------------------------------------------------------------------------------------------------<div>Yue-Wen FANG, PhD candidate<br>
<div><a href="http://clpm.ecnu.edu.cn/" style="font-family:arial,sans-serif;font-size:14px;background-color:rgb(255,255,255)" target="_blank">Key Laboratory of Polar Materials and Devices, Ministry of Education</a><br style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:14px;background-color:rgb(255,255,255)">
<div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:14px;background-color:rgb(255,255,255)"><a href="http://english.ecnu.edu.cn/" target="_blank">East China Normal University </a></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:14px;background-color:rgb(255,255,255)">
<br></div></div><div><br></div><div><br></div></div></div>
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