# DXA

Quote from tengfei zheng on November 26, 2021, 10:22 amDear Constanze & Alex,

I have a problem while using the DXA modifier. Can I count the edge and screw dislocation densities with the different frames? I can't find the answers on the website ovito.modifiers — OVITO Scripting Reference 3.6.0 documentation.

I'm sorry if I don't describe the problem clearly. Really appreciate your help!

Best wishes!

Tengfei Zheng

Dear Constanze & Alex,

I have a problem while using the DXA modifier. Can I count the edge and screw dislocation densities with the different frames? I can't find the answers on the website ovito.modifiers — OVITO Scripting Reference 3.6.0 documentation.

I'm sorry if I don't describe the problem clearly. Really appreciate your help!

Best wishes!

Tengfei Zheng

Quote from Alexander Stukowski on November 26, 2021, 2:20 pmHi,

I'm not sure what your precise goal is. Typically dislocations are curved and never exactly "edge" or "screw". They typically have some mixed character, which means the angle formed by the Burgers vector and the local line tangent is in the range 0° < Θ < 90°. In other words, it doesn't make much sense in my eyes to count dislocations for which the angle is exactly 0° or exactly 90°. One has to look at the distribution of angles instead.

See the attached figure, for example, which is taken from https://www.nature.com/articles/nature23472 (Extended Data Figure 8: Evolution of dislocation characters under compression at rate ×25.)

Is this the type of statistical analysis you have in mind? If yes, then Ovito cannot compute this kind of histogram directly. The program only gives you the line segments each dislocation is made of and the corresponding Burgers vectors (in the simulation coordinate system). However, it's not too difficult to calculate the distribution of line length vs. character angle from this information outside of Ovito.

-Alex

Hi,

I'm not sure what your precise goal is. Typically dislocations are curved and never exactly "edge" or "screw". They typically have some mixed character, which means the angle formed by the Burgers vector and the local line tangent is in the range 0° < Θ < 90°. In other words, it doesn't make much sense in my eyes to count dislocations for which the angle is exactly 0° or exactly 90°. One has to look at the distribution of angles instead.

See the attached figure, for example, which is taken from https://www.nature.com/articles/nature23472 (Extended Data Figure 8: Evolution of dislocation characters under compression at rate ×25.)

Is this the type of statistical analysis you have in mind? If yes, then Ovito cannot compute this kind of histogram directly. The program only gives you the line segments each dislocation is made of and the corresponding Burgers vectors (in the simulation coordinate system). However, it's not too difficult to calculate the distribution of line length vs. character angle from this information outside of Ovito.

-Alex

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