[Wien] Fwd: Strain
Muhammad Sajjad
sajjadpu at gmail.com
Mon Dec 7 11:59:17 CET 2015
Thank you very much Dr. Martin Pieper. Yes phonon calculations speak about
stability of structure but not about breaking point.
On Mon, Dec 7, 2015 at 1:22 PM, pieper <pieper at ifp.tuwien.ac.at> wrote:
> 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 <fecher at 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-bounces at zeus.theochem.tuwien.ac.at
>>> [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Muhammad
>>> Sajjad [sajjadpu at 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
>>> <fecher at uni-mainz.de<mailto:fecher at 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-bounces at zeus.theochem.tuwien.ac.at<mailto:
>> wien-bounces at zeus.theochem.tuwien.ac.at>
>>
>>>
>>> [wien-bounces at zeus.theochem.tuwien.ac.at<mailto:
>> wien-bounces at zeus.theochem.tuwien.ac.at>]
>>
>>> im Auftrag von Muhammad Sajjad
>>> [sajjadpu at gmail.com<mailto:sajjadpu at 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.
>>> _______________________________________________
>>> Wien mailing list
>>>
>>> Wien at zeus.theochem.tuwien.ac.at<mailto:Wien at zeus.theochem.tuwien.ac.at>
>>
>>>
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>>>
>>> --
>>> Kind Regards
>>> Muhammad Sajjad
>>> Post Doctoral Fellow
>>> KAUST, KSA.
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien [1]
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>>
>>> [2]
>>>
>>
>> --
>>
>> Kind Regards
>> Muhammad Sajjad
>> Post Doctoral Fellow
>> KAUST, KSA.
>>
>> Links:
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--
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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