[Pw_forum] Young's Modulus

[mohsen modaresi]

Dear all,
Can Q. E calculate Young's Modulus?
Thanks for your reply

-- 
Mohsen Modarresi,
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131
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[Pw_forum] Young's Modulus

[Stefano Baroni]

Mohsen: I think you can answer by yourself to your question.
Answer this question first:
1) How is the Young's modulus defined?
Ask then yourself the following question:
Can the ingredients entering the answer to question #1 be calculated by QE?
Please, revert to us with the answer to the above chain of questions.
SB

On Sep 21, 2010, at 9:41 AM, mohsen modaresi wrote:

> Dear all,
> Can Q. E calculate Young's Modulus? 
> Thanks for your reply
> 
> -- 
> Mohsen Modarresi,
> PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
> Phone +98-9133452131
> 
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni 
(skype)

La morale est une logique de l'action comme la logique est une morale de la 
pens?e - Jean Piaget

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html







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[Pw_forum] Young's Modulus

[Eyvaz Isaev]

From: mohsen modaresi 
 
>Can Q. E calculate Young's Modulus? 

No,  no ab initio  program can  calculate E directly. You have to calculate 
elastic constants and then you can easily get the Young modulus.
See papers:  Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in 
Intermetallic Compounds: Principles and Practice, vol.1, Principles, J.H. 
Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London, 1995), ch.9 (pp. 
195-210). Search 

cst-www.nrl.navy.mil/users/mehl/papers/cij452.ps.gz via google.

Bests,
Eyvaz.

 ---
Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 
Sweden 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 
Russia, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com



  
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[Pw_forum] Young's Modulus

[Mike Mehl]

We've changed the link slightly.  It's now:

http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf

On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
>
> 
> *From:* mohsen modaresi 

> See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
> Intermetallic Compounds: Principles and Practice, vol.1, Principles,
> J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
> 1995), ch.9 (pp. 195-210).

-- 
Michael J. Mehl
Head, Center for Computational Materials Science
Naval Research Laboratory Code 6390
Washington DC

[Pw_forum] Young's Modulus

[mohsen modaresi]

Dear Stefano, Eyvaz and Mike,
Thanks for your reply. I follow this procedure and get Young's Modulus for
CNT (3,3):
1) relax the structure.
2) compressed the structure in Z direction (parallel to the axis of
nanotube) and calculate "Force" between atoms and then calculate the Young's
Modulus by using it's definition (  E=(F/A)/((L-L0)/L0)  ). The result has
"good" agreement with reported one.
But one of my friend work with Abinit. Abinit can calculate elastic constant
in a systematic way.
Dr. Eyvaz Isaev thanks for the link.




On Tue, Sep 21, 2010 at 5:09 PM, Mike Mehl wrote:

> We've changed the link slightly.  It's now:
>
> http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf
>
> On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
> >
> > 
> > *From:* mohsen modaresi 
>
> > See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
> > Intermetallic Compounds: Principles and Practice, vol.1, Principles,
> > J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
> > 1995), ch.9 (pp. 195-210).
>
> --
> Michael J. Mehl
> Head, Center for Computational Materials Science
> Naval Research Laboratory Code 6390
> Washington DC
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>



-- 
Mohsen Modarresi,
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131
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[Pw_forum] Young's Modulus

[Stefano Baroni]

The application of linear response theory to the calculation of elastic 
constants implemented in abinit was introduced by Giannozzi, Testa, and myself 
soon after our paper on linear-response theory, back in 1987 (PRL 59m p. 2662), 
and rediscovered a few years ago in the abinit group. We never implemented our 
LRT approach because we always thought that, beside elegance, LRT had few 
advantages with respect to the brute-force calculation of the elastic 
constants. We may be wrong, and if anybody volunteers to implement this old 
idea of ours, I would be delighted to help. In any case, I would be curious to 
know if the "systematic" calculation of elastic constants in abinit is any 
faster than what you can get "by hands" either using QE. Cheers - SB

On Sep 22, 2010, at 3:45 PM, mohsen modaresi wrote:

> Dear Stefano, Eyvaz and Mike,
> Thanks for your reply. I follow this procedure and get Young's Modulus for 
> CNT (3,3):
> 1) relax the structure.
> 2) compressed the structure in Z direction (parallel to the axis of nanotube) 
> and calculate "Force" between atoms and then calculate the Young's Modulus by 
> using it's definition (  E=(F/A)/((L-L0)/L0)  ). The result has "good" 
> agreement with reported one. 
> But one of my friend work with Abinit. Abinit can calculate elastic constant 
> in a systematic way.
> Dr. Eyvaz Isaev thanks for the link.
> 
>   
> 
> 
> On Tue, Sep 21, 2010 at 5:09 PM, Mike Mehl  
> wrote:
> We've changed the link slightly.  It's now:
> 
> http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf
> 
> On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
> >
> > 
> > *From:* mohsen modaresi 
> 
> > See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
> > Intermetallic Compounds: Principles and Practice, vol.1, Principles,
> > J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
> > 1995), ch.9 (pp. 195-210).
> 
> --
> Michael J. Mehl
> Head, Center for Computational Materials Science
> Naval Research Laboratory Code 6390
> Washington DC
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
> 
> 
> 
> -- 
> Mohsen Modarresi,
> PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
> Phone +98-9133452131
> 
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni 
(skype)

La morale est une logique de l'action comme la logique est une morale de la 
pens?e - Jean Piaget

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html







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[Pw_forum] Young's Modulus

[Eyvaz Isaev]

Hi,

Yes, you are right about Abinit for elastic constants calculations. The main 
question is which method (Abinit or via total energy) is easier 

and less time-consuming. 

Bests,

Eyvaz.---
Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 
Sweden 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 
Russia, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com





From: mohsen modaresi 
To: PWSCF Forum 
Sent: Wed, September 22, 2010 5:45:14 PM
Subject: Re: [Pw_forum] Young's Modulus

Dear Stefano, Eyvaz and Mike,
Thanks for your reply. I follow this procedure and get Young's Modulus for CNT 
(3,3):
1) relax the structure.
2) compressed the structure in Z direction (parallel to the axis of nanotube) 
and calculate "Force" between atoms and then calculate the Young's Modulus by 
using it's definition (  E=(F/A)/((L-L0)/L0)  ). The result has "good" 
agreement 
with reported one. 

But one of my friend work with Abinit. Abinit can calculate elastic constant in 
a systematic way.
Dr. Eyvaz Isaev thanks for the link.

  



On Tue, Sep 21, 2010 at 5:09 PM, Mike Mehl  wrote:

We've changed the link slightly.  It's now:
>
>http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf>
>
>On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
>>
>> 
>> *From:* mohsen modaresi 
>
>
>> See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
>> Intermetallic Compounds: Principles and Practice, vol.1, Principles,
>> J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
>> 1995), ch.9 (pp. 195-210).
>
>--
>Michael J. Mehl
>Head, Center for Computational Materials Science
>Naval Research Laboratory Code 6390
>Washington DC
>
>___
>Pw_forum mailing list
>Pw_forum at pwscf.org
>http://www.democritos.it/mailman/listinfo/pw_forum
>


-- 

Mohsen Modarresi, 
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131



  
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[Pw_forum] Young's Modulus

[Mehmet Topsakal]

Dear Eyvaz,

I think you omitted one more thing to mention. Brute-force method also
allows one to know what he is doing.



On Wed, Sep 22, 2010 at 8:14 PM, Eyvaz Isaev  wrote:

> Hi,
>
> Yes, you are right about Abinit for elastic constants calculations. The
> main question is which method (Abinit or via total energy) is easier
> and less time-consuming.
>
> Bests,
> Eyvaz.
> ---
> Prof. Eyvaz Isaev,
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University,
> Sweden
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
> Russia,
> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>
>
> --
> *From:* mohsen modaresi 
> *To:* PWSCF Forum 
> *Sent:* Wed, September 22, 2010 5:45:14 PM
> *Subject:* Re: [Pw_forum] Young's Modulus
>
> Dear Stefano, Eyvaz and Mike,
> Thanks for your reply. I follow this procedure and get Young's Modulus for
> CNT (3,3):
> 1) relax the structure.
> 2) compressed the structure in Z direction (parallel to the axis of
> nanotube) and calculate "Force" between atoms and then calculate the Young's
> Modulus by using it's definition (  E=(F/A)/((L-L0)/L0)  ). The result has
> "good" agreement with reported one.
> But one of my friend work with Abinit. Abinit can calculate elastic
> constant in a systematic way.
> Dr. Eyvaz Isaev thanks for the link.
>
>
>
>
> On Tue, Sep 21, 2010 at 5:09 PM, Mike Mehl  nrl.navy.mil>wrote:
>
>> We've changed the link slightly.  It's now:
>>
>> http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf>
>>
>> On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
>> >
>> > 
>> > *From:* mohsen modaresi 
>>
>> > See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
>> > Intermetallic Compounds: Principles and Practice, vol.1, Principles,
>> > J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
>> > 1995), ch.9 (pp. 195-210).
>>
>> --
>> Michael J. Mehl
>> Head, Center for Computational Materials Science
>> Naval Research Laboratory Code 6390
>> Washington DC
>> ___
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>>
>
>
>
> --
> Mohsen Modarresi,
> PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
> Phone +98-9133452131
>
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 

Mehmet Topsakal  (Ph.D. Student)
UNAM-Institute of Materials Science and Nanotechnology.
Bilkent University. 06800 Bilkent, Ankara/T?rkiye
Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365
UNAM-web  : www.nano.org.tr
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[Pw_forum] Young's Modulus

[Stefano Baroni]

For that, also LRT akkows one to know what one is doing ... ;-)
SB

On Sep 22, 2010, at 7:30 PM, Mehmet Topsakal wrote:

> Dear Eyvaz,
> 
> I think you omitted one more thing to mention. Brute-force method also allows 
> one to know what he is doing.
> 
> 
> 
> On Wed, Sep 22, 2010 at 8:14 PM, Eyvaz Isaev  wrote:
> Hi,
> 
> Yes, you are right about Abinit for elastic constants calculations. The main 
> question is which method (Abinit or via total energy) is easier 
> and less time-consuming. 
> 
> Bests, 
> Eyvaz.
> ---
> Prof. Eyvaz Isaev, 
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 
> Sweden 
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 
> Russia, 
> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
> 
> 
> From: mohsen modaresi 
> To: PWSCF Forum 
> Sent: Wed, September 22, 2010 5:45:14 PM
> Subject: Re: [Pw_forum] Young's Modulus
> 
> Dear Stefano, Eyvaz and Mike,
> Thanks for your reply. I follow this procedure and get Young's Modulus for 
> CNT (3,3):
> 1) relax the structure.
> 2) compressed the structure in Z direction (parallel to the axis of nanotube) 
> and calculate "Force" between atoms and then calculate the Young's Modulus by 
> using it's definition (  E=(F/A)/((L-L0)/L0)  ). The result has "good" 
> agreement with reported one. 
> But one of my friend work with Abinit. Abinit can calculate elastic constant 
> in a systematic way.
> Dr. Eyvaz Isaev thanks for the link.
> 
>   
> 
> 
> On Tue, Sep 21, 2010 at 5:09 PM, Mike Mehl  
> wrote:
> We've changed the link slightly.  It's now:
> 
> http://cst-www.nrl.navy.mil/users/mehl/papers/cij453.pdf>
> 
> On 09/21/2010 08:44 AM, Eyvaz Isaev wrote:
> >
> > 
> > *From:* mohsen modaresi 
> 
> > See papers: Mehl et al., PhysRev.B 41, 10311, 1990 and Mehl et al, in
> > Intermetallic Compounds: Principles and Practice, vol.1, Principles,
> > J.H. Wesbrook and R.L. Fleischer, eds, John Wiley and Sons (London,
> > 1995), ch.9 (pp. 195-210).
> 
> --
> Michael J. Mehl
> Head, Center for Computational Materials Science
> Naval Research Laboratory Code 6390
> Washington DC
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
> 
> 
> 
> -- 
> Mohsen Modarresi,
> PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
> Phone +98-9133452131
> 
> 
> 
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
> 
> 
> 
> 
> -- 
> 
> Mehmet Topsakal  (Ph.D. Student)
> UNAM-Institute of Materials Science and Nanotechnology. 
> Bilkent University. 06800 Bilkent, Ankara/T?rkiye
> Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365
> UNAM-web  : www.nano.org.tr
> 
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni 
(skype)

La morale est une logique de l'action comme la logique est une morale de la 
pens?e - Jean Piaget

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html







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[Pw_forum] Young's Modulus

[Eduardo Ariel Menendez Proupin]

Hi,
I think we always know what WE do, but not all of what computers do :-(.

Mohsen, did you relaxed the atoms after the compression? Why did you
calculate force and not stress. Have you used a finite nanotube and computed
the forces upon the atoms of the edge? Finally, how is defined A in
E=(F/A)/((L-L0)/L0)
for the case of a single nonotube?
Best regards
Eduardo

Eduardo Menendez
Departamento de Fisica
Facultad de Ciencias
Universidad de Chile
Phone: (56)(2)9787439
URL: http://fisica.ciencias.uchile.cl/~emenendez

Let's pray for the 33 trapped miners! Four months to rescue



> -- Mensaje reenviado --
> From: Stefano Baroni 
> To: PWSCF Forum 
> Date: Wed, 22 Sep 2010 19:43:15 +0200
> Subject: Re: [Pw_forum] Young's Modulus
> For that, also LRT akkows one to know what one is doing ... ;-)
> SB
>
> On Sep 22, 2010, at 7:30 PM, Mehmet Topsakal wrote:
>
> Dear Eyvaz,
>
> I think you omitted one more thing to mention. Brute-force method also
> allows one to know what he is doing.
>
>
>
> On Wed, Sep 22, 2010 at 8:14 PM, Eyvaz Isaev wrote:
>
>> Hi,
>>
>> Yes, you are right about Abinit for elastic constants calculations. The
>> main question is which method (Abinit or via total energy) is easier
>> and less time-consuming.
>>
>> Bests,
>> Eyvaz.
>> ---
>> Prof. Eyvaz Isaev,
>> Department of Physics, Chemistry, and Biology (IFM), Linkoping University,
>> Sweden
>> Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
>> Russia,
>> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>
>
>>
-- 


.
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[Pw_forum] Young's Modulus

[mohsen modaresi]

Dear Eduardo Ariel Menendez Proupin,
At first i relaxed nano-tube and obtain the position of carbon atoms in the
ground state. Then i decrease the tube length. A in the relation is the area
of nano-tube (A=pi*R*R which R is the radius of tube). F is the atomic force
in the Z axis which can be calculated by using Q.E.
I think it is better to calculate total energy in some configuration and use
(F=dE/dz, where E is the total energy in different configuration).
Is there any problem in this procedure?



On Thu, Sep 23, 2010 at 12:58 AM, Eduardo Ariel Menendez Proupin <
eariel99 at gmail.com> wrote:

> Hi,
> I think we always know what WE do, but not all of what computers do :-(.
>
> Mohsen, did you relaxed the atoms after the compression? Why did you
> calculate force and not stress. Have you used a finite nanotube and computed
> the forces upon the atoms of the edge? Finally, how is defined A in   
> E=(F/A)/((L-L0)/L0)
> for the case of a single nonotube?
> Best regards
> Eduardo
>
> Eduardo Menendez
> Departamento de Fisica
> Facultad de Ciencias
> Universidad de Chile
> Phone: (56)(2)9787439
> URL: 
> http://fisica.ciencias.uchile.cl/~emenendez<http://fisica.ciencias.uchile.cl/%7Eemenendez>
>
> Let's pray for the 33 trapped miners! Four months to rescue
>
>
>
>> -- Mensaje reenviado --
>>
>> From: Stefano Baroni 
>> To: PWSCF Forum 
>> Date: Wed, 22 Sep 2010 19:43:15 +0200
>>
>> Subject: Re: [Pw_forum] Young's Modulus
>> For that, also LRT akkows one to know what one is doing ... ;-)
>> SB
>>
>> On Sep 22, 2010, at 7:30 PM, Mehmet Topsakal wrote:
>>
>> Dear Eyvaz,
>>
>> I think you omitted one more thing to mention. Brute-force method also
>> allows one to know what he is doing.
>>
>>
>>
>> On Wed, Sep 22, 2010 at 8:14 PM, Eyvaz Isaev 
>> wrote:
>>
>>> Hi,
>>>
>>> Yes, you are right about Abinit for elastic constants calculations. The
>>> main question is which method (Abinit or via total energy) is easier
>>> and less time-consuming.
>>>
>>> Bests,
>>> Eyvaz.
>>> ---
>>> Prof. Eyvaz Isaev,
>>> Department of Physics, Chemistry, and Biology (IFM), Linkoping
>>> University, Sweden
>>> Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
>>> Russia,
>>> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>>
>>
>>>
> --
>
>
> .
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 
Mohsen Modarresi,
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131
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[Pw_forum] Young's Modulus

[mohsen modaresi]

Dear Eduardo Ariel Menendez Proupin,
I forget to answer other questions.
If we relaxed the tube after compression there is no net force on carbon
atoms so I did not relax the system after compression.
*Have you used a finite nanotube and computed the forces upon the atoms of
the edge?*.> A finite nano-tube? I consider a unit cell (which can make
an infinite tube ) and calculate force between atoms.
Is there any problem?

Mohsen Modarresi

On Thu, Sep 23, 2010 at 1:21 AM, mohsen modaresi
wrote:

> Dear Eduardo Ariel Menendez Proupin,
> At first i relaxed nano-tube and obtain the position of carbon atoms in the
> ground state. Then i decrease the tube length. A in the relation is the area
> of nano-tube (A=pi*R*R which R is the radius of tube). F is the atomic force
> in the Z axis which can be calculated by using Q.E.
> I think it is better to calculate total energy in some configuration and
> use (F=dE/dz, where E is the total energy in different configuration).
> Is there any problem in this procedure?
>
>
>
> On Thu, Sep 23, 2010 at 12:58 AM, Eduardo Ariel Menendez Proupin <
> eariel99 at gmail.com> wrote:
>
>> Hi,
>> I think we always know what WE do, but not all of what computers do :-(.
>>
>> Mohsen, did you relaxed the atoms after the compression? Why did you
>> calculate force and not stress. Have you used a finite nanotube and computed
>> the forces upon the atoms of the edge? Finally, how is defined A in   
>> E=(F/A)/((L-L0)/L0)
>> for the case of a single nonotube?
>> Best regards
>> Eduardo
>>
>> Eduardo Menendez
>> Departamento de Fisica
>> Facultad de Ciencias
>> Universidad de Chile
>> Phone: (56)(2)9787439
>> URL: 
>> http://fisica.ciencias.uchile.cl/~emenendez<http://fisica.ciencias.uchile.cl/%7Eemenendez>
>>
>> Let's pray for the 33 trapped miners! Four months to rescue
>>
>>
>>
>>> -- Mensaje reenviado --
>>>
>>> From: Stefano Baroni 
>>>  To: PWSCF Forum 
>>> Date: Wed, 22 Sep 2010 19:43:15 +0200
>>>
>>> Subject: Re: [Pw_forum] Young's Modulus
>>> For that, also LRT akkows one to know what one is doing ... ;-)
>>> SB
>>>
>>> On Sep 22, 2010, at 7:30 PM, Mehmet Topsakal wrote:
>>>
>>> Dear Eyvaz,
>>>
>>> I think you omitted one more thing to mention. Brute-force method also
>>> allows one to know what he is doing.
>>>
>>>
>>>
>>> On Wed, Sep 22, 2010 at 8:14 PM, Eyvaz Isaev 
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> Yes, you are right about Abinit for elastic constants calculations. The
>>>> main question is which method (Abinit or via total energy) is easier
>>>> and less time-consuming.
>>>>
>>>> Bests,
>>>> Eyvaz.
>>>> ---
>>>> Prof. Eyvaz Isaev,
>>>> Department of Physics, Chemistry, and Biology (IFM), Linkoping
>>>> University, Sweden
>>>> Theoretical Physics Department, Moscow State Institute of Steel &
>>>> Alloys, Russia,
>>>> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>>>
>>>
>>>>
>> --
>>
>>
>> .
>>
>>
>> ___
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>>
>>
>
>
> --
> Mohsen Modarresi,
> PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
> Phone +98-9133452131
>
>


-- 
Mohsen Modarresi,
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131
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[Pw_forum] Young's Modulus

[Eduardo Ariel Menendez Proupin]

Dear Mohsen

Let me comment on your procedure

>At first i relaxed nano-tube and obtain the position of carbon atoms in the
>ground state. Then i decrease the tube length. A in the relation is the
area of >nano-tube (A=pi*R*R which R is the radius of tube). F is the atomic
force in >the Z axis which can be calculated by using Q.E.
>I think it is better to calculate total energy in some configuration and
use >(F=dE/dz, where E is the total energy in different configuration).
>Is there any problem in this procedure?

First, are you calculating the Young modulus of an isolated nanotube, or of
a material composed of (3,3) nanotubes perfectly oriented and with a well
defined density ?

The Young modulus is a concept that is well suited for a homogeneous
material, e.g., a bulk of nanotubes. It will depend on the density and
orientations of the nanotubes, but will be indendent of the transverse area
(the force and the energy of deformation is prportional to the area). In a
bulk of nanotubes perfectly oriented, the relevant area A would be the
transverse area of the unit cell, and the size and shape of the  unit cell
depends on the density of nanotubes, or must be optimized by a mimimum
energy criterium. If you are studying the Young modulus of a single isolated
nanotube, then note that the Young modulus is well defined only if everybody
use the same definition of A. Hence, be sure of considering the same
definition as the other results that you compare. Second, be sure to use a
unit cell sufficiently wide,  so that the preriodic replicas of the nanotube
are far enough and  the results do not depend on the transversal dimensions
of the unit cell.


>If we relaxed the tube after compression there is no net force on carbon
>atoms so I did not relax the system after compression.
*>Have you used a finite nanotube and computed the forces upon the >atoms of
the edge?*.> A finite nano-tube? I consider a unit cell (which can >make
an infinite tube ) and calculate force between atoms.
>Is there any problem?
Yes. The state with the atoms not relaxed is not a state of equilibrium, and
according to Boltzmann law, if its energy difference with the relaxed state
is larger than kT (0.026 eV at 300 K), this state may happen only once in
the lifetime of the universe. Then, the property you calculate may have
nothing to do with a real situation. Hence, relax the atoms.

If you relax, of course  there will be no net force upon the atoms, but the
tube have stress. Use tstress=.true. and use the appropriate  component of
the stress tensor as F/A. Remember to do it for various transverse sizes of
the simulation cell and be sure that the stress is independent of the cell
size, or extrapolate. Of course, also must be independent of the cutoffs and
smearing parameters (degauss). Alternatively, you may use the second
derivative of the total energy to obtain the Young modulus. It is healthy to
use both methods to check that the results are fine. The numbers will not be
exactly equal due to numerical reasons, and you can systematically improve
the agreement increasing the cutoffs and the number of kpoints.


When I asked about a finite nanotube, I was thinking in an alternative way
to do it. Use a large cubic cell, with a finite nanotube inside, made a
constrained relaxation fixing the z coordinate (I assume that z is the
nanotube axis) of the edge atoms, relax the other atoms, and sum the forces
acting upon the atoms at one edge (that must be the negative of the total
force upon the other edge). With that you can obtain the Young modulus of a
finite nanotube. If you want it for the infinite nanotube you must do it
with several lengths and extrapolate to infinite length. Of course this is
much more  expensive (really brute force) if your goal is the infinite
nanotube, but is is what you should do if your interest is in short
nanotubes.

Best regards
Eduardo

-- 


Eduardo Menendez
Departamento de Fisica
Facultad de Ciencias
Universidad de Chile
Phone: (56)(2)9787439
URL: http://fisica.ciencias.uchile.cl/~emenendez

Let's pray for the 33 trapped miners! Four months to rescue.
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[Pw_forum] Young's Modulus

[mohsen modaresi]

Dear Eduardo Ariel Menendez Proupin,
Thanks for your useful comments.
Mohsen

On Thu, Sep 23, 2010 at 12:56 PM, Eduardo Ariel Menendez Proupin <
eariel99 at gmail.com> wrote:

> Dear Mohsen
>
> Let me comment on your procedure
>
> >At first i relaxed nano-tube and obtain the position of carbon atoms in
> the >ground state. Then i decrease the tube length. A in the relation is the
> area of >nano-tube (A=pi*R*R which R is the radius of tube). F is the atomic
> force in >the Z axis which can be calculated by using Q.E.
> >I think it is better to calculate total energy in some configuration and
> use >(F=dE/dz, where E is the total energy in different configuration).
> >Is there any problem in this procedure?
>
> First, are you calculating the Young modulus of an isolated nanotube, or of
> a material composed of (3,3) nanotubes perfectly oriented and with a well
> defined density ?
>
> The Young modulus is a concept that is well suited for a homogeneous
> material, e.g., a bulk of nanotubes. It will depend on the density and
> orientations of the nanotubes, but will be indendent of the transverse area
> (the force and the energy of deformation is prportional to the area). In a
> bulk of nanotubes perfectly oriented, the relevant area A would be the
> transverse area of the unit cell, and the size and shape of the  unit cell
> depends on the density of nanotubes, or must be optimized by a mimimum
> energy criterium. If you are studying the Young modulus of a single isolated
> nanotube, then note that the Young modulus is well defined only if everybody
> use the same definition of A. Hence, be sure of considering the same
> definition as the other results that you compare. Second, be sure to use a
> unit cell sufficiently wide,  so that the preriodic replicas of the nanotube
> are far enough and  the results do not depend on the transversal dimensions
> of the unit cell.
>
>
> >If we relaxed the tube after compression there is no net force on carbon
> >atoms so I did not relax the system after compression.
> *>Have you used a finite nanotube and computed the forces upon the >atoms
> of the edge?*.> A finite nano-tube? I consider a unit cell (which can
> >make an infinite tube ) and calculate force between atoms.
> >Is there any problem?
> Yes. The state with the atoms not relaxed is not a state of equilibrium,
> and according to Boltzmann law, if its energy difference with the relaxed
> state is larger than kT (0.026 eV at 300 K), this state may happen only once
> in the lifetime of the universe. Then, the property you calculate may have
> nothing to do with a real situation. Hence, relax the atoms.
>
> If you relax, of course  there will be no net force upon the atoms, but the
> tube have stress. Use tstress=.true. and use the appropriate  component of
> the stress tensor as F/A. Remember to do it for various transverse sizes of
> the simulation cell and be sure that the stress is independent of the cell
> size, or extrapolate. Of course, also must be independent of the cutoffs and
> smearing parameters (degauss). Alternatively, you may use the second
> derivative of the total energy to obtain the Young modulus. It is healthy to
> use both methods to check that the results are fine. The numbers will not be
> exactly equal due to numerical reasons, and you can systematically improve
> the agreement increasing the cutoffs and the number of kpoints.
>
>
> When I asked about a finite nanotube, I was thinking in an alternative way
> to do it. Use a large cubic cell, with a finite nanotube inside, made a
> constrained relaxation fixing the z coordinate (I assume that z is the
> nanotube axis) of the edge atoms, relax the other atoms, and sum the forces
> acting upon the atoms at one edge (that must be the negative of the total
> force upon the other edge). With that you can obtain the Young modulus of a
> finite nanotube. If you want it for the infinite nanotube you must do it
> with several lengths and extrapolate to infinite length. Of course this is
> much more  expensive (really brute force) if your goal is the infinite
> nanotube, but is is what you should do if your interest is in short
> nanotubes.
>
> Best regards
> Eduardo
>
> --
>
>
> Eduardo Menendez
> Departamento de Fisica
> Facultad de Ciencias
> Universidad de Chile
> Phone: (56)(2)9787439
> URL: 
> http://fisica.ciencias.uchile.cl/~emenendez
>
> Let's pray for the 33 trapped miners! Four months to rescue.
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 
Mohsen Modarresi,
PhD student of Solid State Physics, Ferdowsi University of Mashhad, Iran.
Phone +98-9133452131
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