[Pw_forum] CNT unit cell vectors

[xirainbow]

> what is the difference between scf and relax calculations since all DFT are 
> self consistent?
 In relax calculation, atoms move to decrease the energy.
 In scf, atoms are fixed.

> I found carbon nanotubes input files using ibrav=6 and others using ibrav=8, 
> so how can I which one I should use?
As long as the distance between neighboring CNT is big
enough, you can choose any one.




On Sun, Jun 16, 2013 at 2:00 AM, Mahmoud Hammouri  wrote:
> Thank you Wang for you answer. I found carbon nanotubes input files using
> ibrav=6 and others using ibrav=8, so how can I which one I should use?
> Another question: what is the difference between scf and relax calculations
> since all DFT are self consistent?
>
> Mahmoud
>
> On Jun 15, 2013, at 4:03, "pw_forum-request at pwscf.org"
>  wrote:
>
> Wang
>
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum



-- 

Hui Wang
School of physics, Fudan University, Shanghai, China

[Pw_forum] CNT unit cell vectors

[Mahmoud Hammouri]

Thank you Wang for you answer. I found carbon nanotubes input files using 
ibrav=6 and others using ibrav=8, so how can I which one I should use? Another 
question: what is the difference between scf and relax calculations since all 
DFT are self consistent?

Mahmoud

On Jun 15, 2013, at 4:03, "pw_forum-request at 
pwscf.org" mailto:pw_forum-request at pwscf.org>> wrote:

Wang
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[Pw_forum] CNT unit cell vectors

[xirainbow]

Dear Mahmoud Hammouri:
   For Tetragonal P, "a" must be equal to "b". Therefore, it
is forbidden to set "b" as an individual variable.
   For an isolated CNT, you can set "a" arbitrarily. But the
condition is not true for "c" ("c" is along the axis of CNT ). The
length of "c" of CNT changes much with the chiral angle of CNT.


On Fri, Jun 14, 2013 at 5:22 PM, Mahmoud Hammouri  wrote:
> Hi all,
> I have problem for defining the lattice vectors of carbon nanotubes, I saw
> some examples for zigzag CNTs and they are using ibrav =6 with celldm(1)=31
> and celldm(3)= 0.25 and in another file celldm(3)=0.1704 I'm really wonder
> why they did not define celldm(2)? Now, for more than one unit cell how
> celldm(3) would change.
> In the descriptions of the pw.x input file, for Tetragonal P (st):
>  celldm(3)=c/a and since c=1.42 and a=4.26 then celldm(3)=0.333 not 0.25 or
> 0.17 as others said!!!
>
>
> Regards
>
> ___
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum



-- 

Hui Wang
School of physics, Fudan University, Shanghai, China

[Pw_forum] CNT unit cell vectors

[Mahmoud Hammouri]

Hi all,
I have problem for defining the lattice vectors of carbon nanotubes, I saw some 
examples for zigzag CNTs and they are using ibrav =6 with celldm(1)=31 and 
celldm(3)= 0.25 and in another file celldm(3)=0.1704 I'm really wonder why they 
did not define celldm(2)? Now, for more than one unit cell how celldm(3) would 
change.
In the descriptions of the pw.x input file, for Tetragonal P (st):
 celldm(3)=c/a and since c=1.42 and a=4.26 then celldm(3)=0.333 not 0.25 or 
0.17 as others said!!!


Regards
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