This question was also asked on the Vesta Users' forum:
Using the software Vesta for drawing crystal structures, it is possible to draw coordination polyhedra around selected atoms. The polyhedron usualy consists of several faces with the coordinating atoms at the corner of the faces and of the polyhedron itself. It appears that VESTA defines distinct faces such that the bounding atoms are located in a common plane. This is always the case for three atoms. If the coordination polyhedron, is however a cube, four corner atoms form the square faces. This is indeed the case, if you try to plot the coordination cube of an Ca atom in the Fluorite (CaF2) structure. If you have, however, a cube in a low-symmetry structure, such that the atoms making a square of a cube are not exactly in a plane, it appears that Vesta requires the four atoms to be located exactly in a plane. Otherwise the square bounding a cubic is divided into two triangles. I have illustrated this problem in an artificial structure in the attached picture: right an ideal cube, left a cube, where the cubic symmetry was artificially broken by slightly shifting one of the atoms. Thereby, the four atoms of the face indicated with the arrow become slightly "out-of-plane". The dihedral angle is about 0.1°.
My Question: is it possible to set a minimum threshold value for the dihedral angle such that several triangle form a larger polygon (tetragon, pentagon, hexagon) bounding my coordination polyhedron? I think to remember than in Diamond (?) there was such an option.
Best regards
Andreas Leineweber
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