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### Messages - jchang

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1
##### Questions and Answers / meaning of energy cutoff value for LCAO DFT calculation
« on: November 12, 2020, 09:35 »
Hi,

I have a basic question about energy cutoff.
Basically, energy cutoff defines the energy limit for plane wave basis set.
Then, what is the meaning of energy cut off if I use LCAO basis set for DFT?
Can anyone explain this?

Thanks.
jiwon

2
##### Questions and Answers / Re: Ge Bandstructure pps-PBE
« on: October 12, 2020, 01:44 »
Thanks Anders. It works!

3
##### Questions and Answers / Ge Bandstructure pps-PBE
« on: October 7, 2020, 08:58 »
Hi,

I have a question on Ge band structure calculation shown in this link.
https://docs.quantumatk.com/tutorials/dft_half_pps/dft_half_pps.html

I tried to follow the calculations using files (bulks.py, pbe.py, pps.py) which I can download from the above link.
I could run pbe.py, but I got into licence error issue when I tried to run pps.py which is for adjusting the Ge band gap.
To run pps-DFT, do we need a special license for ATK?

Can you please give me any advices on this issue?

Thanks.
jiwon

4
##### Questions and Answers / Unit of Transmission
« on: January 28, 2020, 13:38 »
Hi

I have question about the unit of transmission which we get from the transmission calculation.
Let's say that we have periodic structure in transverse direction like an example below.
https://docs.quantumatk.com/tutorials/transmission_gr_mos2/transmission_gr_mos2.html
And I want to calculate current/width [A/um].
Then, the transmission that I get from the calculation in the above example should be divided by the width of real space unit cell. (of course, I need to multiply it with e^2/h)
Am I doing right?
I just want to confirm the dimension of the transmission that I get from quantum ATK.

Thanks.
jiwon

5
##### Questions and Answers / SCF converge issue in Optimization
« on: September 25, 2019, 23:59 »
Hi

I am trying to do geometry optimization of a certain 3 layers of 2D materials.
I have issue in the scf convergence.
To resolve the scf convergence issue, I tried to increase k point and energy cut off. But both didn't work for my case.
I attached my input file of 9x9x1 k point and output log file.
In the first several scf loop converge, but it fails.
I have tested increased k point, but the result is same.

Please give me any advices to solve scf issue in optimization.

Thanks.
jiwon

6
##### Questions and Answers / Re: work function of bulk material
« on: August 30, 2019, 04:23 »
I see.  Thanks for your response.
Do you mean that quantumATK cannot calculate work function for bulk?

7
##### Questions and Answers / Re: work function of bulk material
« on: August 28, 2019, 09:26 »
Thanks for the quick response.
Then, for the bulk work function calculation, do I need to set up a thick slab to mimic the bulk and then do the work function calculation?

8
##### Questions and Answers / work function of bulk material
« on: August 28, 2019, 07:02 »
Hi,

I want to know how to calculate the work function of bulk material.
ATK tutorial about calculating work function is for slab structure having vacuum. And it seems that vacuum is required to set a energy reference.
However, in bulk system, since we don't have vacuum, it is hard to set up any reference by setting up boundary condition.
So, can  we calculate work function of bulk material with ATK?

Thanks.
jiwon

9
##### Questions and Answers / Re: unit of transmission spectrum and DOS
« on: July 9, 2019, 10:30 »
Thanks for the fast response.
So, you are saying that the transmission and DOS value from ATK is not normalized by length or area.

Thanks.
jiwon

10
##### Questions and Answers / unit of transmission spectrum and DOS
« on: July 9, 2019, 08:15 »
Hi,

I have a question about the unit of transmission in the example below.

https://docs.quantumwise.com/tutorials/transmission_gr_mos2/transmission_gr_mos2.html

In this example, we calculate transmission of rectangular unit cell of graphene and MoS2.
In the graphene example, it shows how transmission spectrum changes with the number of k-points in the transverse modes.
And my question is what is the unit of Transmission.
Since it is a periodic structure in the transverse direction, transmission unit should be #/m or #/um, but the picture showing transmission it is not clear.

Is the default unit in the transmission spectrum just # or #/m?
If it is just #, then I guess we need to divide it with the length of rectangular unit cell in the transverse direction (y-direction).

I also have similar question for DOS calculation.
If I calculate DOS for 2-D material, then the unit for the calculated DOS in ATK is just #/eV or is it normalized with area?

Thanks.
jiwon

11
##### Questions and Answers / Re: monolayer MoS2 electron affinity calculation
« on: June 29, 2019, 10:42 »
Thanks for the confirmation!

12
##### Questions and Answers / Re: monolayer MoS2 electron affinity calculation
« 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

13
##### Questions and Answers / Re: monolayer MoS2 electron affinity calculation
« 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

14
##### Questions and Answers / Re: monolayer MoS2 electron affinity calculation
« 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

15
##### Questions and Answers / 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

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