Author Topic: Geometry Optimization in Germanene Zigzag nanoribbon incorrect results  (Read 169 times)

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Offline agoldsto

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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.


Offline Troels-Markussen

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Hi,

It seems that your unit cell in the C-direction for the ZZNR is too long, since there are no bonds in the C-direction crossing the unit cell edge. I would guess your structure should look more like the attached figure.

Regards,
Troels

Offline agoldsto

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EDIT: Problem solved, thank you for the assistance
« Last Edit: September 21, 2020, 03:00 by agoldsto »