QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Ashley.amanta@gmail.com on June 10, 2017, 08:59
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Hi
I want to relax a MoS2 nanoribbon.I need sitting and parameters for New calculater and Geometryoptimization blocks for that.please help me how I can relax that?
Thank you!
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If I do the relaxation of MoS2 nanoribbon, I used to relax the MoS2 monolayer with the smallest unit cell. After that, I will directly repeat the unit cell to form the nanoribbon without any further relaxation. As to the parameters for doing the relaxation, I think GGA-SG15-medium is sufficient for this system. I like to use a k-point sampling of (9 9 1) (for hexagonal unit cell) and 0.01/0.001 for force tolerance and stress tolerance, respectively.
I also want to know if it is appropriate.
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For general OptimizeGeometry settings, please consult our tutorial on this: http://docs.quantumwise.com/tutorials/geometry_optimization/geometry_optimization.html
For calculator settings, you can either look for tutorials involving 2D materials and use those to get started, and/or start by using default values, and then make sure to converge them.
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It really depends on what you want to simulate by doing these calculations. Nanoribbons are usually placed on a substrate that may constrain the nanoribbon structure in some way. It can also be an unsupported or partly supported nanoribbon. You would perhaps need to make the choice yourself, based on your research goals and scientific intuition.
The tutorial with an example of how to do geometry optimization is mentioned in one of the previous posts.
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It can be inferred from your last picture that the original configuration of your system is a nanosheet. If you want to simulate a nanoribbon, you need to add sufficient vacuum on both side of one direction (B or C) to form a nanoribbon.
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It's indeed a nanosheet, or a monolayer since it is periodic along B and C directions. If you want to get a nanoribbon, you need to add vacuum along one of the direction. Please see attached .py file.
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I think the vacuum in your structure along B direction is not sufficient. I just increased the vacuum to a larger value. You can set the vector B to a larger value of 30, or 40 as you like.
The tutorial you referred to is dealing with a MoS2 nanotube. It's different with a nanoribbon.
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To optimize the geometry of a nanoribbon is just like that we need to do geometry optimization for a monolayer. It's not a problem or a strange phenomenon that the edge state of the nanoribbon will change after the geometry optimization.