Author Topic: Void in amorphous material  (Read 111 times)

jhart

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Void in amorphous material
« on: November 13, 2017, 07:46:43 PM »
How can I identify void formation in an amorphous material using OVITO? Is there a computation that can identify regions that are much less dense than others?


Alexander Stukowski

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Re: Void in amorphous material
« Reply #1 on: November 17, 2017, 11:41:52 AM »
Hi,

there are two approaches that come to my mind:

(1) You can use OVITO's Voronoi Analysis function to compute the atomic volume. The volume per atom can be taken as a local measure of the density. Note that it might be necessary to flatten out local fluctuations. This can be done using the Compute Property modifier or the Bin and Reduce modifier.

(2) The Construct Surface Mesh modifier allows you to reconstruct the outer and inner surfaces of a solid. Hence, it can be used to identify pores in a material. Here, the probe sphere radius parameter of the modifier controls the minimum size of the pores to be identified.

jhart

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Re: Void in amorphous material
« Reply #2 on: December 06, 2017, 06:22:53 PM »
If I use the Voronoi analysis modifier, I see that it outputs atomic volume, which gives a local measure of the density. You said that I can use the bin and reduce modifier to flatten out local fluctuations. Once I go to Bin and Reduce, and select Atomic Volume under particle property, Which Reduction operation should I use, and which binning direction should I use?

Will this output something new that I Can use under particle selection? How specifically can I determine the less-dense regions and thus a void?

Thanks for your help!

Alexander Stukowski

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Re: Void in amorphous material
« Reply #3 on: December 10, 2017, 06:20:19 PM »
The Bin and Reduce function can map the per-atom volumes only to a two-dimensional grid of bins, not a three-dimensional one. So averaging will be performed within each bin and along the third axis. I don't know, this may not be the best choice for you problem at hand. It makes most sense for situations that are quasi-two-dimensional.

With the Compute Property modifier you can do a three-dimensional spatial averaging around each atom. Imagine a sphere with a user-defined radius around each atom. The value at every central site is computed as the sum over the values of all atoms contained within the sphere. In a second step, you can divide the summed values by the number of atoms in each sphere, giving you average values.