[QE-users] Carbon Nanotube work function calculation

[John Travers]

 Hi Dominik
Thank you very much for the detailed explanation! Really appreciated!

When you say " you can directly use the Fermi energy of said calculation and the vacuum energy you get from the
planar average to calculate your work function.", I understand that my vacuum level should be derived from the planar average, however, in the planar average procedure, the code needs the awin input. From your suggestion, it seems that I can input as zero. Did I get this right?
Best
J. Tong


    On Wednesday, July 8, 2020, 02:19:27 AM EDT, <dv009200 at fh-muenster.de> wrote:  
 
 The average electrostatic potential you are calculating with average.x
does show microscopic oscillations that represent the atomic planes of
your system (planar averages --> the 2d column as a function of the 1st
one in your avg.out file).

The calculation of the work function needs a fixed energy level to compare
the bulk and the slab calculation (as it is done in the Workfunction
example in the PP folder). Therefor you run a macroscopic average of the
x-y averaged electrostatic potential. The window you choose for the
macroscopic average (this is your awin parameter) is just the distance
between two consecutive atomic planes (in a.u.). So that microscopic
oscillations with period of awin are averaged and a constant level (in the
inner region of the slab) is obtained.

In your case I don't think it makes sense to compare the CNT calculation
(or monolayer graphene) to a bulk system, so that you can directly use the
Fermi energy of said calculation and the vacuum energy you get from the
planar average to calculate your work function.

Since this is not my field of expertise maybe someone else can comment on
this topic.

Best regards

Dominik


Dominik Voigt
PhD Student University of Applied Sciences Münster
Department of Physical Chemistry


>
> Thanks Dominik!
> The awin parameter is confusing to me for the 1d and 2d system. For a CNT
> calculation using unit cell (with large enough vacuum space), is awin the
> diameter of nanotube?
> J. Tong
>    On Tuesday, July 7, 2020, 04:37:48 AM EDT, <dv009200 at fh-muenster.de>
> wrote:
>
>  If your CNT has already enough vacuum space in x and y direction so that
> periodic images won't interact which each other you don't need to repeat
> your cell in that directions.
> This is 'only' a Bachelor thesis but it might help you getting started:
> http://web.mit.edu/janetryu/Public/finalthesis.pdf
>
> For the meaning of the input parameters you can check the average.f90 file
> normally there is a satisfactorily explanation.
>
> Best regards
>
> Dominik
>
>
> Dominik Voigt
> PhD Student University of Applied Sciences Münster
> Department of Physical Chemistry
>
>> Dear All
>> I tried to use QE to compute the work function for some metallic single
>> wall nanotubes. I studied the workfunction example provided by the QE
>> code, and searched in the QE user archives where I found some useful
>> descriptions on the calculation of work function, but I am still
>> confused
>> with the calculation and the average procedure for the general 1D and 2D
>> systems. My specific questions are:
>> 1. should I construct a supercell to perform the calculation? For
>> nanotube
>> (1D system), assuming that the z-direction is periodic,  should I
>> construct a supercell by repeating in one of the other directions (x, or
>> y)?
>> 2. When performing planar average, I am confused the awin parameter. For
>> the supercell, is awin the distance between the two nearest neighboring
>> nanobtubes?
>> 3. For a 2D system, for example a mono-layer graphene, how do I define
>> awin?
>> Thank you for your help!
>>
>> J. Tong
>> Master Student, Chemistry DepartmentHenan Normal
>> University_______________________________________________
>> Quantum ESPRESSO is supported by MaX
>> (www.max-centre.eu/quantum-espresso)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users


_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
users mailing list users at lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200708/8bac93f8/attachment.html>