Coordination number for BCC structure when performing Voronoi analysis

Dear all,

I constructed a BCC monocrystal with periodic boundary conditions for both Fe and V, and then minimized its energy at 0 K. When performing Voronoi analysis using Ovito-3.10.6, the calculated coordination number was 14! This number was still 14 for tested BCC bicrystal systems. To my understanding, the coordination number for BCC should theoretically be 8. While the calculated coordination number for FCC structure was 12, which is equal to the theoretical value.
I just cannot figure out what leads to this phenomenon. Could anyone please provide me some suggestions. Thanks in advance!

Best regards,

If you pick a single particle and visualize its Voronoi bonds it’s easier to see that the Voronoi cell of a BCC particle is a truncated octahedron with 6 faces with 4 edges and 8 faces with 6 edges: <0 0 0 6 0 8>, which in sum are 14 faces = coordination number. Here the shape of the Voronoi cell is determined by the 8 nearest neighbors (yellow) and 6 next-nearest neighbors (blue).

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What you probably want to do is use the Coordination analysis modifier.
If you set the cut-off radius to a value just slightly larger than the first neighbor distance, you’ll notice that the Coordination property output by this modifier is 8 for a perfect BCC system.

Hi Kalcher,

Thank you very much for clarifying this issue. I will modify the Coordination analysis accordingly to yield the desired results.