Author Topic: monolayer MoS2 electron affinity calculation  (Read 160 times)

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Offline jchang

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monolayer MoS2 electron affinity calculation
« on: June 19, 2019, 04:27 »
Hi

I tried to calculate the electron affinity for monolayer MoS2.
I used informations which I could find in the link below.
https://forum.quantumatk.com/index.php?topic=5270.msg23352#msg23352
https://forum.quantumatk.com/index.php?topic=5114.msg22147#msg22147
https://docs.quantumwise.com/tutorials/work_function_ag_100/work_function_ag_100.html#work-function-ag-100

I want to confirm that what I did is right.
I introduce one sulfer ghost atom and set the boundary conditions as mentioned in the tutorial.
Then, I ran chemical potential calculation.

I attatch my script file here. Please take a look and let me know if this approach is right.

Thanks.
jiwon

Offline Petr Khomyakov

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Re: monolayer MoS2 electron affinity calculation
« Reply #1 on: June 24, 2019, 10:22 »
You may first run the script, get the results and analyze them, and do benchmarking if something is known in literature about work function and/or affinity of this material.  That would allow you to validate your approach/script.

Offline jchang

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Re: monolayer MoS2 electron affinity calculation
« Reply #2 on: June 24, 2019, 11:28 »
Thanks for your response.

I ran it and found the obtained affinity is same with what I could get from other experiment and calculations of monolayer MoS2.
But, this one does not guarantee that my approach is right. As mentioned in the one of the link in my original post, we can get the value from the wrong approach. That is why I ask an expert's advice.

jiwon

Offline Petr Khomyakov

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Re: monolayer MoS2 electron affinity calculation
« Reply #3 on: June 24, 2019, 11:47 »
As mentioned in the one of the link in my original post, we can get the value from the wrong approach.
Please describe your issue in more detail. It is not clear what you refer to in the previous posts .   

Offline jchang

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Re: monolayer MoS2 electron affinity calculation
« Reply #4 on: June 24, 2019, 12:47 »
I see. Sorry for not to be clear on the question.
Let me specify it.

So, in the example of Ag work function calculation as below
https://docs.quantumwise.com/tutorials/work_function_ag_100/work_function_ag_100.html#work-function-ag-100

It set up one Ag atom as a ghost.

To do the same thing on monolayer MoS2, I put atoms as follows

vacuum Mo-S-Mo-Mo(ghost atom) vacuum

Monolayer Mo-S-Mo is there and one Mo atom is placed on one side of MoS2.
Then, here what could be the good distance between MoS2 and ghost Mo atom? Any distance would be fine?
One more question is
Do I need to run relaxation calculation (relaxing Mo-S-Mo and fix ghost Mo atom)?
If I have relaxed Mo-S-Mo (monolayer MoS2), then placing one ghost Mo atom requires another relaxation?

Thanks.
jiwon


Offline Petr Khomyakov

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Re: monolayer MoS2 electron affinity calculation
« Reply #5 on: June 27, 2019, 01:02 »
I would first try to do calculations without ghost atoms, and then see how introduction of ghost atoms affects the affinity value. It is hard to say which position of ghost atoms is "good", without doing any calculations.

In general, LCAO basis set is tricky to use for affinity/work function calculations, especially, for open structures such as MoS2, i.e., not closed-packed structures such as Ag surface, for example, or other metal surfaces where position of ghost atoms is somewhat obvious. For accurate calculations, you may however try using plane-wave basis set (also available in QuantumATK) that does not require any ghost atoms to describe wave function tails in the vacuum far from the surface.
« Last Edit: June 27, 2019, 01:06 by Petr Khomyakov »

Offline jchang

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Re: monolayer MoS2 electron affinity calculation
« Reply #6 on: June 27, 2019, 02:31 »
Thanks for your response.

So, if we use plane-wave basis,  we don't need ghost atom and setting up boundary conditions (top side of supercell to Dirichlet, bottom side of superccell to Neumann) would give a right chemical potential.
Is this right?

Thanks.
jiwon

Offline Petr Khomyakov

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Re: monolayer MoS2 electron affinity calculation
« Reply #7 on: June 27, 2019, 21:29 »
Yes, that is correct.

Offline jchang

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Re: monolayer MoS2 electron affinity calculation
« Reply #8 on: June 29, 2019, 10:42 »
Thanks for the confirmation!