I Primitive unit cell (Diamond)

  • Thread starter Porkaborg
  • Start date
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Summary
Primitive unit cell of diamond, great confusion.
Hi guys , I want to construct a primitive unit cell for diamond, which is made of a fcc lattice and a basis of 2 carbons atoms. I know that a primitive unit cell isn't unique but the two variants I get are drastically different . As far as I can see they both include 2 whole atoms/points in the lattice, however one of them occupies 1/4 of the conventional-cell volume, and the other occupies 1/8 of the conventional-cell volume.

When I couldn't get further in reasoning, I tried googling it and found both versions listed as primitive unit cells for diamond. But I am still confused why they look so very different.
(The left picture doesn't include rest of the atoms for some reason but they are there before creating the primitive unit cell)

Skærmbillede 2019-10-04 kl. 22.48.17.png
Skærmbillede 2019-10-04 kl. 22.45.25.png


I hope someone can point out the difference , or pinpoint why I may be confused, please comment if I need to add some additional info.
 

DrDu

Science Advisor
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How do you want to fill space with only translated copies of a tetrahedron?
 
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I guess I can't , which is needed to fulfill the definition of a unitcell. Thanks a lot DrDu!. Upon looking some more at it , the tetrahedron also doesn't include a single lattice point which it is supposed to do to be a primitive unit cell.
 

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