<div dir="ltr">Thank you very much <span style="font-size:12.8000001907349px">Dr. Martin Pieper. Yes phonon calculations speak about stability of structure but not about breaking point. </span></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Dec 7, 2015 at 1:22 PM, pieper <span dir="ltr"><<a href="mailto:pieper@ifp.tuwien.ac.at" target="_blank">pieper@ifp.tuwien.ac.at</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello Muhammad!<br>
<br>
A DFT code will not simply say *crack* at some point of strain. Wien2k will always distribute the force you apply according to the perfect translational symmetry of your crystal structure - in contrast to nature where things like cracking or breaking occure at weak links - points where this translational symmetry is broken and the bonding is weaker.<br>
<br>
DFT will do its very best to distribute the electrons in any structure you throw at it and tell you (an upper bound of) the minimum energy of the configuration. I am no expert but I understand that from a calculated variation of total energy with lattice parameter you can estimate the intrinsic strength of a structure within some model for the process.<br>
<br>
In addition Wien2k gives information where the total energy is stored, for example the forces on atoms in your structure. Therefore, if you look at the total energy of your strained structure you will see that it is larger - at 5% distortion perhaps considerably so. Depending on site symmetry some calculated internal forces may indicate where in the structure the 'springs' you pulled are located. Furthermore the phonon code might inform you of instabilities in your structure.<br>
<br>
Good luck,<br>
<br>
Martin Pieper<br>
<br>
<br>
---<br>
Dr. Martin Pieper<br>
Karl-Franzens University<br>
Institute of Physics<br>
Universitätsplatz 5<br>
A-8010 Graz<br>
Austria<br>
Tel.: +43-(0)316-380-8564<div><div class="h5"><br>
<br>
<br>
Am 04.12.2015 15:25, schrieb Muhammad Sajjad:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
Dear Tomas and Fecher<br>
Thank you very much. It is working perfect with lattice type F and<br>
symmetry operations equal to 16. But one thing is confusing me that I<br>
applied 5 % strain to bulk Si and still it is semiconductor with gap<br>
0.2eV. Is it correct? as 5 % is too much strain and bulk materials<br>
tolerate very low strain. In my thinking it should break.<br>
<br>
On Fri, Dec 4, 2015 at 5:14 PM, Fecher, Gerhard <<a href="mailto:fecher@uni-mainz.de" target="_blank">fecher@uni-mainz.de</a>><br>
wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
but your structure becomes tetragonal<br>
you should reset the symmetry operations to (generate) to be<br>
recalculated during initialisation<br>
<br>
Ciao<br>
Gerhard<br>
<br>
DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
"I think the problem, to be quite honest with you,<br>
is that you have never actually known what the question is."<br>
<br>
====================================<br>
Dr. Gerhard H. Fecher<br>
Institut of Inorganic and Analytical Chemistry<br>
Johannes Gutenberg - University<br>
55099 Mainz<br>
and<br>
Max Planck Institute for Chemical Physics of Solids<br>
01187 Dresden<br>
________________________________________<br>
Von: <a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a><br>
[<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a>] im Auftrag von Muhammad<br>
Sajjad [<a href="mailto:sajjadpu@gmail.com" target="_blank">sajjadpu@gmail.com</a>]<br>
Gesendet: Freitag, 4. Dezember 2015 15:08<br>
An: A Mailing list for WIEN2k users<br>
Betreff: Re: [Wien] Fwd: Strain<br>
<br>
I am sorry having no idea about it. Simply I used optimized<br>
structure and increased a by a0*1.001 and decreased b & c by keeping<br>
lattice type F. Then run init_lapw -b.<br>
<br>
On Fri, Dec 4, 2015 at 4:51 PM, Fecher, Gerhard<br>
<<a href="mailto:fecher@uni-mainz.de" target="_blank">fecher@uni-mainz.de</a><mailto:<a href="mailto:fecher@uni-mainz.de" target="_blank">fecher@uni-mainz.de</a>>> wrote:<br>
you applied a tetragonal distortion along x<br>
but how did you manage that you still have 48 symmetry operations ?<br>
<br>
Ciao<br>
Gerhard<br>
<br>
DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
"I think the problem, to be quite honest with you,<br>
is that you have never actually known what the question is."<br>
<br>
====================================<br>
Dr. Gerhard H. Fecher<br>
Institut of Inorganic and Analytical Chemistry<br>
Johannes Gutenberg - University<br>
55099 Mainz<br>
and<br>
Max Planck Institute for Chemical Physics of Solids<br>
01187 Dresden<br>
________________________________________<br>
Von:<br>
<br>
</blockquote>
<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a><mailto:<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a>><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
</blockquote>
[<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a><mailto:<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a>>]<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
im Auftrag von Muhammad Sajjad<br>
[<a href="mailto:sajjadpu@gmail.com" target="_blank">sajjadpu@gmail.com</a><mailto:<a href="mailto:sajjadpu@gmail.com" target="_blank">sajjadpu@gmail.com</a>>]<br>
<br>
Gesendet: Freitag, 4. Dezember 2015 14:04<br>
An: wien<br>
Betreff: [Wien] Fwd: Strain<br>
<br>
Dear All<br>
I got Si structure from wien2k examples and after optimization it<br>
is<br>
SILICON<br>
F LATTICE,NONEQUIV.ATOMS: 1<br>
MODE OF CALC=RELA unit=ang<br>
10.305626 10.305626 10.305626 90.000000 90.000000 90.000000<br>
ATOM 1: X=0.12500000 Y=0.12500000 Z=0.12500000<br>
MULT= 2 ISPLIT= 2<br>
1: X=0.87500000 Y=0.87500000 Z=0.87500000<br>
Si NPT= 781 R0=0.00010000 RMT= 2.22 Z:<br>
14.0<br>
LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
0.0000000 0.0000000 1.0000000<br>
48 NUMBER OF SYMMETRY OPERATIONS<br>
<br>
mBJLDA gives band gap of 1.19 eV (perfect).<br>
<br>
Now I apply strain (0.1 %) and structure is<br>
<br>
SILICON<br>
F LATTICE,NONEQUIV.ATOMS: 1<br>
MODE OF CALC=RELA unit=ang<br>
10.315932 10.300477 10.300477 90.000000 90.000000 90.000000<br>
ATOM -1: X=0.12500000 Y=0.12500000 Z=0.12500000<br>
MULT= 2 ISPLIT=-2<br>
-1: X=0.87500000 Y=0.87500000 Z=0.87500000<br>
Si NPT= 781 R0=0.00010000 RMT= 2.22 Z:<br>
14.0<br>
LOCAL ROT MATRIX: 0.0000000 0.0000000 1.0000000<br>
1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
48 NUMBER OF SYMMETRY OPERATIONS<br>
This time band structure (attached herewith) is very different and<br>
Si is metal.<br>
Kindly guide me whether I am apply strain in right way or not? Band<br>
Structure is<br>
<br>
Kind Regards<br>
Muhammad Sajjad<br>
Post Doctoral Fellow<br>
KAUST, KSA.<br>
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Post Doctoral Fellow<br>
KAUST, KSA.<br>
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Kind Regards<br>
Muhammad Sajjad <br>
Post Doctoral Fellow<br>
KAUST, KSA.<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><div>Kind Regards</div><div>Muhammad Sajjad </div><div>Post Doctoral Fellow</div><div>KAUST, KSA.</div></div></div>
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