Hello Muhammad!

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.

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.

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.

Good luck,

Martin  Pieper


---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 04.12.2015 15:25, schrieb Muhammad Sajjad:
Dear Tomas and Fecher
Thank you very much. It is working perfect with lattice type F and
symmetry operations equal to 16. But one thing is confusing me that I
applied 5 % strain to bulk Si and still it is semiconductor with gap
0.2eV. Is it correct? as 5 % is too much strain and bulk materials
tolerate very low strain. In my thinking it should break.

On Fri, Dec 4, 2015 at 5:14 PM, Fecher, Gerhard <fec...@uni-mainz.de>
wrote:

but your structure becomes tetragonal
you should reset the symmetry operations to (generate) to be
recalculated during initialisation

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden
________________________________________
Von: wien-boun...@zeus.theochem.tuwien.ac.at
[wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von Muhammad
Sajjad [sajja...@gmail.com]
Gesendet: Freitag, 4. Dezember 2015 15:08
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] Fwd: Strain

I am sorry having no idea about it. Simply I used optimized
structure and increased a by a0*1.001 and decreased b & c by keeping
lattice type F. Then run init_lapw -b.

On Fri, Dec 4, 2015 at 4:51 PM, Fecher, Gerhard
<fec...@uni-mainz.de<mailto:fec...@uni-mainz.de>> wrote:
you applied a tetragonal distortion along x
but how did you manage that you still have 48 symmetry operations ?

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden
________________________________________
Von:

wien-boun...@zeus.theochem.tuwien.ac.at<mailto:wien-boun...@zeus.theochem.tuwien.ac.at>

[wien-boun...@zeus.theochem.tuwien.ac.at<mailto:wien-boun...@zeus.theochem.tuwien.ac.at>]
im Auftrag von Muhammad Sajjad
[sajja...@gmail.com<mailto:sajja...@gmail.com>]

Gesendet: Freitag, 4. Dezember 2015 14:04
An: wien
Betreff: [Wien] Fwd: Strain

Dear All
I got Si structure from wien2k examples and after optimization it
is
SILICON
F   LATTICE,NONEQUIV.ATOMS:  1
MODE OF CALC=RELA unit=ang
 10.305626 10.305626 10.305626 90.000000 90.000000 90.000000
ATOM   1: X=0.12500000 Y=0.12500000 Z=0.12500000
          MULT= 2          ISPLIT= 2
       1: X=0.87500000 Y=0.87500000 Z=0.87500000
Si         NPT=  781  R0=0.00010000 RMT= 2.22        Z:
14.0
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
  48      NUMBER OF SYMMETRY OPERATIONS

mBJLDA gives band gap of 1.19 eV (perfect).

 Now I apply strain (0.1 %) and structure is

SILICON
F   LATTICE,NONEQUIV.ATOMS:  1
MODE OF CALC=RELA unit=ang
 10.315932 10.300477 10.300477 90.000000 90.000000 90.000000
ATOM  -1: X=0.12500000 Y=0.12500000 Z=0.12500000
          MULT= 2          ISPLIT=-2
      -1: X=0.87500000 Y=0.87500000 Z=0.87500000
Si         NPT=  781  R0=0.00010000 RMT= 2.22        Z:
14.0
LOCAL ROT MATRIX:    0.0000000 0.0000000 1.0000000
                     1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
  48      NUMBER OF SYMMETRY OPERATIONS
This time band structure (attached herewith) is very different and
Si is metal.
Kindly guide me whether I am apply strain in right way or not? Band
Structure is

Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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--
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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Kind Regards
Muhammad Sajjad 
Post Doctoral Fellow
KAUST, KSA.

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