Topics

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General Questions and Answers / Calculate Local Density of States perpendicular to device transport direction

« on: September 23, 2021, 18:21 »

Hello, I have a zigzag germanene nanoribbon device and am able to calculate LDOS and PDOS in the transport (z) direction (results attached), but I am interested in the LDOS in the perpendicular (x) direction to show evidence of the quantum spin hall effect. However the LDOS calculations seem to automatically choose the transport direction and I can't figure out how to change that. Is it possible to do so in ATK? Any assistance is greatly appreciated, thank you

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General Questions and Answers / LDOS Calculation for Edge-Passivated Germanene Nanoribbons

« on: August 28, 2021, 21:18 »

Hello, I'm trying to obtain an LDOS graph like the one shown below for edge passivated germanene nanoribbons. I've attached a picture of one of my nanoribbons passivated with Sulfur. I have extended the length by repeating the cell 10 times in the C direction, but I cannot select the bulk to device option. I only need Vds, no gate voltage required. I've looked into the issue, and my concern is the solutions I've found for creating the source and drain regions may change the nanoribbon by either removing the sulfur passivated atoms at the electrodes or required a different structure than armchair germanene. If my goal is to obtain an LDOS vs thickness graph for the attached nanoribbon, how should I approach this? Thank you[img]

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General Questions and Answers / Issues with geometry optimization of Iodine passivated Germanene Nanoribbon

« on: February 28, 2021, 19:46 »

Hello, I'm doing studies on edge passivation of Germanene Nanoribbons using a variety of elements. With Hydrogen Geometry optimization went smoothly, but I'm struggling to get a good result with Iodine as the passivating element. I'm using the same settings as I did for Hydrogen, that is:

- Rattle atoms prior to script generator
- In the New Calculator Block use: ATK-DFT, GGA-PBE Correlation, 75 Hartree density mesh cutoff, 1x21x21 k-points, Tight Tier 1 basis set (I have also tried double zeta polarized)
- In the geometry optimization block use: 0.01 Force Tolerance, 0.0005 Stress Tolerance, 200 steps, max step size of 0.5A, constrain cell in x direction

I have also tried adjusting the lattice parameters to increase size of unit cell prior to calculations and various force and stress tolerance values. I get different results, but all clearly incorrect. Any advice would be appreciated.

I've attached an image of the nanoribbon prior to rattling and optimization, and the post optimization result

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General Questions and Answers / How to do geometry optimization for OH molecule attached to Carbon Nanotube

« on: February 4, 2021, 04:37 »

Hello, I'm trying to see the impact of attaching OH to carbon nanotubes of various chiralities. I want to perform geometry optimization for the OH molecule as the carbon nanotube has already been relaxed, however I'm not sure what the best approach is, currently I'm doing DFT-LDA with dirichlet boundary conditions in the A and B direction with periodic in the C direction, and constraining all directions in geometry optimization. Again, I performed the relaxation on the nanotube before adding the OH group. Any assistance would be appreciated!

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General Questions and Answers / Geometry Optimization in Germanene Zigzag nanoribbon incorrect results

« on: August 31, 2020, 02:27 »

Hello, I'm doing research on Germanene nanoribbons. Germanene is predicted to have buckling of roughly 0.7 angstroms in the honeycomb lattice. When I performed geometry optimization on the Germanene Armchair nanoribbon from the plugin the buckling appeared and had the proper displacement. However when I do the same optimization on the zig zag armchair it remains flat, which I don't believe should be accurate. Do you know why this could be or what settings I should change to get the proper output? Below are pictures of the armchair and zigzag nanoribbon results and the calculation parameters. The pictures show the front and side view of the armchair nanoribbon post optimization and the zigzag nanoribbon before optimization. Post optimization is looks exactly the same except the hydrogen atoms have a 45 degree tilt to the left. It is still completely flat.

The calculation parameters for both optimizations were the same, ATK-DFT GGA with Tight Tier 1 as the basis set. For the geo optimization block I used a Force Tolerance of 0.01 eV/A and for the Stress Tolerance 0.0005 eV/A^3. Step size was 0.5 and the simulation was tested with the cell constrained in only the x direction and no constraints at all. Both provided the same result.

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General Questions and Answers / Bandstructure of 5 atom Germanene AC Nanoribbon

« on: April 25, 2020, 22:47 »

I'm doing research on the properties of Germanene nanoribbons and encountered a result that my advisor found questionable. For the four atom AC nanoribbon, the bandgap is roughly 0.8eV, and we're trying to shrink that. However when I increase the width by a single atom, it decreases to 0.08eV. My advisor says this is too small to be accurate, and mentioned using the quantum mechanical model in ATK. It's not a problem I've been able to solve by hand, so what options are available for a more comprehensive band structure analysis? Where can I find information on adding the quantum mechanical model to my calculation, and does this bandgap seem reasonable? Any help would be appreciated.

For my bandstructure calculator, in the new calculator box I used the Extended Huckel with no SCF iteration and dirichlet boundary conditions for the regions bounded by hydrogen. For the bandstructure I used the simple bandstructure box and 200 points per segment. I shared pictures of my results below. I used geometry optimization to obtain the buckling, and share pictures of both the 4 atom nanoribbon and 5 atom one, with bandstructures for both.