Topics

1

General Questions and Answers / Algorithm used for calculating DOS and PDOS in ATK

« on: March 5, 2019, 14:27 »

Does ATK use Wang and Landau algorithm for calculating DOS? How does Tetrahedron method calculate DOS? Can someone refer me to some article or book where i can read about the associated theory?

2

General Questions and Answers / DOS of MoS2/Au interpretation

« on: March 3, 2019, 12:43 »

I did a DOS calculation of monolayer MoS2/Au system with thick vacuum (35 Ang) on the c direction. I got DOS like the one shown in figure. But in the band gap region, I don't get any region with 0 DOS for MoS2/Au system. My structure also does not seem like it has been optimized (not much change in position of Au atoms) although the geometry optimization showed that the structure has been optimized.

My question is, if I give the vacuum region too much, is it going to affect my calculations? And if yes, then why? I suppose if larger the vaccum, the better it is for Veff to decay smoothly.

3

General Questions and Answers / Bravais lattice type for DOS calculation

« on: February 16, 2019, 11:43 »

Hi,

I have a monolayer MoS2 with 6 Au layer structure. But the unit cell type after interface formation is "Unit Cell". For DOS calculation should it be changed to some other Lattice type like that of MoS2 (Hexagonal).  If not, in DOS calculator, it asks for shifting the Gamma point, so how is the k-point decided for this unit cell?

4

General Questions and Answers / Checking strain of a molecule on a surface

« on: February 4, 2019, 12:27 »

I am studying the effect of presence of metals like Cr, Al etc. on top of monolayer MoS2. I want to see the strain with different crystal orientation of metals before I perform geometry optimization.

For this I used Builder > Interface. I placed monolayer MoS2 (with c = 50 Ang) on first drop zone and bulk metals (with different crystal orientation) in second drop zone. This gives me the strain on first zone as 0 % and second zone shows some strain. Is this strain value of the interface or simply of the bulk metal?

Will this strain value have same magnitude when I convert the bulk metal to molecule and place it randomly on top of MoS2?

5

General Questions and Answers / Geometry optimization not converging

« on: January 31, 2019, 07:23 »

I have a 5x5 supercell monolayer MoS2, on top of it I have placed 2 Cr atoms (cleaved along 100) after converting them into molecule. I want to study the effect of Cr on DOS of MoS2. But the geometry optimization didn't converge. Any inputs?

6

General Questions and Answers / Pseudopotential to use for Cr metal

« on: January 30, 2019, 13:29 »

Which pseudopotential should be used for metal (Cr)? I am performing geometry optimization with Cr molecule on top of monolayer MoS2 and using OMX pseudopotential for Mo and S atoms.

7

General Questions and Answers / SCF calculation during DOS calculation

« on: January 30, 2019, 07:21 »

I have optimized the geometry of a 5x5 MoS2 monolayer supercell with a Sulfur vacancy. Now I need to find out its DOS, do I need to perform the SCF iteration again?

8

General Questions and Answers / Simulating Chromium thermal evaporation at different pressure on MoS2 FET

« on: January 30, 2019, 06:55 »

I want to simulate the thermal evaporation of Chromium under different pressure conditions for achieving good contact resistance and also perform transport calculations. How can this be achieved in ATK?

9

General Questions and Answers / Calculation of defect density in MoS2 due to sulfur vacancy

« on: January 28, 2019, 14:51 »

I have a 3x3 supercell of MoS2. I have removed the S atom from the center  I want to calculate the defect density so that in my simulation, I can match it to the sulfur vacancy defect density in exfoliated 2H MoS2. Any inputs on how can I calculate it?

10

General Questions and Answers / Ionic Liquid based 2D FET

« on: January 24, 2019, 19:07 »

Is it possible in ATK to have a drop of Ionic Liquid (IL) like EMI-TFSI, DEME-TFSI etc. on top of my 2D material based FET for studying transport phenomenon?
I checked the database but there are no ILs present. If this is not possible, I was thinking of creating a slab around the channel and defining dielectric constant inside the slab equal to dielectric constant of  IL and then apply a very high transverse E field.  This will somewhat emulate an IL gated FET. But in order to increase carrier concentration in the channel, the channel needs to be doped. I don't understand how this doping should be done.

Can this slab idea be implemented in ATK?

11

General Questions and Answers / Bulk MoS2 band gap

« on: January 18, 2019, 07:19 »

Hi,

I am using QuantumATK 2017.2 version. I am doing band structure calculation for bulk MoS2. I am using ATK-DFT: LCAO, GGA-PBE exchange-correlation, 75 Ha mesh cutoff, 8x8x8 k point, OMX pseudopotential with Medium basis set. But I get band gap 0.89 eV rather than 1.2 eV.

12

General Questions and Answers / Geometry optimization

« on: November 6, 2018, 16:16 »

When evaluating the band structure or doing any calculation in ATK, why is it necessary to do a geometry optimization? The unit cell dimensions and distance between atoms is already determined from X-ray diffraction experiments and we have a list of all those data. Then why is geometry optimization required?

Can someone explain the process what background calculation is done at the back end to optimize the geometry. I want to know after each geometry is the KS equation solved and Hamiltonian determined to find the lowest energy/minimum force between atoms?

13

General Questions and Answers / MoS2 orientation for band structure

« on: September 3, 2018, 15:50 »

If i am doing only band structure calculation, is it necessary to align the z direction in MoS2 plane?
I am referring to step 3 in Geometry for MoS2, https://docs.quantumwise.com/tutorials/transmission_gr_mos2/transmission_gr_mos2.html

14

General Questions and Answers / Decreasing number of bands in bandstructure

« on: September 3, 2018, 13:01 »

I am plotting the bandstrucutre of monolayer MoS2 of a 4x4 supercell. I chose 10 points per segment, Bands above fermi level: automatic and default k points. I get too many bands and also not getting the direct band gap value at the K point. How to reduce the number of bands? I have attached the input file for optimization and band-structure input file. I used LCAO with GGA-PBE method with cut-off 55 Hartree. Broadening was 1000 K (I don't understand what this is?)

15

General Questions and Answers / Space group of Monolayer MoS2

« on: September 3, 2018, 08:53 »

Hi,

I imported the cif file for 2H MoS2 which included 1 unit cell having 2 layers of MoS2. The space group was 194. In order to make it a monolayer, I deleted the other set of atoms and just repeated my lattice in a and b directions to have a monolayer. But then the space group was changed to 187. Why is the space group changing? Does this still represent the true monolayer MoS2?