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work function with ESM model
Date: 2018/08/01 10:59
Name: jiang

Dear OpenMX users,

I am trying to calculate workfunction and electron affinity of materials. I read this thread:

http://www.openmx-square.org/forum/patio.cgi?mode=view&no=1586

If using ESM model, I think there is no need to use empty atoms?

Can I use on1 or on4 with zero potential? Are they equivalent?

I also read this slide

https://gist.github.com/Ncmexp2717/eceeac40c55153374fda4824e173720b/raw/7cfaa1fd89bf4418769777979b7a7d607d6c9dfe/slide_wf_reduced.pdf

I have some difficulty understanding the second figure. Why does it plot Pd100.v0-vxc0.wf and how to relate v0 with Fermi level to get workfunction?

Thank you very much for help.

Best,
Z Jiang
メンテ
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Re: work function with ESM model ( No.1 )
Date: 2018/08/01 12:37
Name: Naoya Yamaguchi

Dear Jiang,

I made the slide and the following are my answers:

>If using ESM model, I think there is no need to use empty atoms?

I think you should use empty atoms to describe the states outside the surface accurately. Comparing pp. 7 (without empty atom) with 10 (with empty atoms) in my slide, values of the work function varies as widely as about 0.3-0.5 eV in M(111) (M=Al, Cu, Ag, Au).


>Can I use on1 or on4 with zero potential? Are they equivalent?

The values "on1" and "on4" are not equivalent. The following page in the section of ESM in the manual says "where on1, on2, on3, and on4 represent combinations of ESMs, 'vacuum + vacuum', 'ideal metal + ideal metal', 'vacuum + ideal metal', and 'ideal metal + ideal metal under an electric field', respectively.":
http://www.openmx-square.org/openmx_man3.8/node138.html


>I have some difficulty understanding the second figure. Why does it plot Pd100.v0-vxc0.wf and how to relate v0 with Fermi level to get workfunction?

I plotted the difference between "v0" and "vxc0" (Pd100.v0-vxc0.wf) and sum of "vna" and "vhart" (Pd100.vna+vhart.wf) to show a relation: "v0=vhart+vna+vxc0" in an informal seminar in our laboratory.
According to a thread below:
http://www.openmx-square.org/forum/patio.cgi?mode=view&no=1587
, you can find a relation between potential terms:
v0=vhart+vna+vxc0.
And you can find the fermi level as "Chemical potential" in *.out file.

Regards,
Naoya Yamaguchi
メンテ
Re: work function with ESM model ( No.2 )
Date: 2018/08/02 03:01
Name: jiang

Hi Naoya san,

Thank you for the explanation. In your slide, it is said work function is expressed as energy difference between the vacuum level φ∞ and Fermi level EF. In slide 3, the equation shows vacuum level is calculated from max Veff.

What I am confused is Veff had non-local part, which is not in v0 file. And why in another thread it is again said vacuum level is calculated from vhart?

Best,
Z Jiang
メンテ
Re: work function with ESM model ( No.3 )
Date: 2018/08/02 08:33
Name: jiang

Hi,

Just to make sure. If I used the ESM on1 scheme, then the vacuum level is fixed at zero. So 0 - Fermi energy equals to the work function. Is this correct?

Best,
Z Jiang
メンテ
Re: work function with ESM model ( No.4 )
Date: 2018/08/02 16:17
Name: Naoya Yamaguchi

Dear Jiang,

>What I am confused is Veff had non-local part, which is not in v0 file.

Your point is correct, for v0 file doesn't include the non-local part. However, the non-local part soon vanishes with respect to r (the distance from an ion core) as you can see in Fig. (b) in the following:
http://www.openmx-square.org/adpack_man2.2/node10.html

And, you can check this from *.vps file (including the pseudopotential), and I leave the URL of a thread about a format of *.vps file for your information:
http://www.openmx-square.org/forum/patio.cgi?mode=view&no=1414

>And why in another thread it is again said vacuum level is calculated from vhart?

As you can see the figure about vna, vhart, and vxc0, that is, each component of v0 in my slide, the vacuum level seems to be able to be calculated using any potential file. (Note: In my knowledge, vhart is not V_{Hartree} in my slide. The manual (http://www.openmx-square.org/openmx_man3.8/node25.html) says as follows:
- System.Name.vhart.cube
The Hartree potential in a Gaussian cube format.

, but I believe it is not correct because its Japanese version says (http://www.openmx-square.org/openmx_man3.8jp/node25.html):
- System.Name.vhart.cube
The difference charge density Hartree potential from the difference charge density is preserved (my translation).
(Google Translate: Differential electron Hartree potential generated from the difference electron density is preserved.)

And, according to the technical note (http://www.openmx-square.org/tech_notes/tech1-1_2.pdf),
VH is decomposed into two contributions V(a)H and δVH(r) coming from the superposition of atomic charge densities and the difference charge density δn(r).
)

>If I used the ESM on1 scheme, then the vacuum level is fixed at zero. So 0 - Fermi energy equals to the work function. Is this correct?

I think so, and in my experience, I actually calculate the work function from only the Fermi energy, but I don't know how the origin of the energy is fixed when one use the ESM scheme.

Regards,
Naoya Yamaguchi
メンテ
Re: work function with ESM model ( No.5 )
Date: 2018/08/03 04:14
Name: jiang

Dear Naoya san,

Thank you very much! It is very clear now.

Best,
Z Jiang
メンテ

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