Messages

1

General Questions and Answers / Density mesh cut-off for mgga

« on: December 8, 2017, 06:54 »

Hello,
I had analysed optical spectrum for phosphorene using mgga with two different values of density mesh cut-off (60 and 90 hartree) keeping all other values same for both the cases. The results had huge difference.
What value should we keep for cut-off for the optimum results and how do we decide for it?

2

General Questions and Answers / Refractive index

« on: October 14, 2017, 11:35 »

Hi sir,

What is refractive index? what is the significance of it and how can we explain the graph of refractive index obtained from VNL-ATK?

Thanks

3

General Questions and Answers / Doubt regarding Bandgap

« on: October 12, 2017, 11:43 »

Hello Sir,
With reference to paper "DOI: 10.1039/C7CP03960C", I tried calculating the band gap of the blue phosphorene and MoSe2 after interfacing them at the optimized interlayer distance of 3.8A.
I had tried with many combinations (SG15, FHI) and with strict mesh cut-offs but I was getting the 'indirect Band gap' unlike what the paper mentions of getting the 'direct band gap'.
Surprisingly  I tried with a different brillouin route (default - 'G, Z') and was getting a 'direct band gap' of 1.45eV (paper mentions 1.1eV).
My doubt is whether band gap depends on the brillouin route and if yes then what route should be selected for the reliable results?

4

General Questions and Answers / Re: Heterostructure and interlayer distance

« on: October 11, 2017, 09:51 »

Thank you again sir.

5

General Questions and Answers / Re: Heterostructure and interlayer distance

« on: October 10, 2017, 18:24 »

Sir,
With reference to your earlier reply, I had tried for different heterostructures so that I can be sure of the results. Also, in my last reply  I had mentioned the paper for the '2.5A' thing. This 2.5A distance is for MoS2/stanene heterostructure.
I was trying the method for different structures so that before asking you I may be sure of the method I am performing.

Thank you for your time and suggestion.
Any  advice will be really helpful.

6

General Questions and Answers / Re: Heterostructure and interlayer distance

« on: October 9, 2017, 16:51 »

Thank you for the suggestion sir.

I tried manual scanning as well. But the paper results are different.
Taking example of a paper DOI: 10.1088/1361-6528/aa68d8,
there in the graph shown for binding ergy. V/s interlayer distance, the minimum energy is at at 2.8A. But when I had tried to check, it was ~8.89eV and when divided by total atoms it was around -88meV but they are reporting  -144meV.
Also i tried with one more heterostructure and it was revealing -160meV B.E. and paper was mentioning ~40meV.
Is it because of another tool they are using and could I go with my results.
Please suggest me.

7

General Questions and Answers / Creating stanene

« on: October 6, 2017, 19:48 »

Hello sir,
How can we create a unit cell of stanene? Is it possible to create using the same procedure as for silicene, as in one of the tutorials? If yes , then does it too requires few times perturbation as in silicene?

8

General Questions and Answers / Re: Heterostructure and interlayer distance

« on: October 6, 2017, 15:31 »

Sir,
I have attached the py file.
DOI of reference : 10.1103/PhysRevB.88.085318 .
In the 4th section, in the last line of 1st para, it has mentioned the distance. Also the paper mention distance for mos2/ws2 .

9

General Questions and Answers / Re: Heterostructure and interlayer distance

« on: October 5, 2017, 20:34 »

Hello Sir,
We are trying to make heterostructures and we started with the MoS2 and MoSe2. The experimental value of the interlayer distance between the two is 6.65A. I have 2 questions-

1. I have first increased the 'c' vector for mono layer MoS2 to 23A  and then added MoSe2 to it. By default it aligned itself to almost ~6.65A but when I shifted MoSe2 a bit and then optimized using PBE-D2, then the resultant interlayer distance doesn't come out to be 6.65A rather it remains at the same position it was kept. So how to proceed further in a case where new structure is being made with van der waal forces in between them.
2. Whether interface should be done to avoid the above situation? If yes, then whether lattice vector 'c' for mos2  and should be increased  and then interfaced or directly without increasing?

10

General Questions and Answers / MoS2 bandgap

« on: September 28, 2017, 19:20 »

Hello sir,
I have calculated the bandstructure of monolayer MoS2  using MGGA with basis set Tier 3 for both sulphur and Molybdenum  (pseudopotential- HGH[6] for sulphur and HGH[14] for molybdenum) and getting 1.87 eV band gap.

But when we change the Tier for molybdenum (Tier 4) we got the band gap of 1.79eV .

Please tell me how to select a Tier as basis set in MGGA method.

11

General Questions and Answers / Optical properties

« on: September 27, 2017, 12:53 »

Hello,
I tried to analyse optical spectrum using both exchange correlation 'GGA' & 'MGGA'.
Both results are totally different and GGA is converging fast as compared to MGGA.
Which of the results are reliable - 'GGA' or 'MGGA'?

12

General Questions and Answers / CFA-MoS2 monolayer

« on: September 21, 2017, 19:05 »

Dear users,
I am trying to interface Co2FeAl  (Heusler alloy) with MoS2 using the interface tool. The problem being faced is that the interatomic displacement option in the 'Shift Surface' parameter is not active and in the ATK-Forcefield as well, there is no literature present for calculating the minimum displacement.
What should be done in order to create an interface?
Any comments would be appreciated.C

13

General Questions and Answers / TiO2 nanotube

« on: September 19, 2017, 22:50 »

Hello Sir,
How can we form a nanotube of TiO2(titania)?
In a tutorial video for a tube of MoS2, they have considered 2,1,0 values for A' in super cell for converting the lattice to orthorhombic. I tried it for the TiO2 but the resultant structure is not satisfactory.

14

General Questions and Answers / TiO2-CQD-TiO2 junction

« on: September 11, 2017, 11:41 »

Dear ATK users,
How to form a nano-composite of TiO2 and carbon quantum dot, where TiO2 are the left and right electrodes, for simulating its one dimensional conductance.