The number of lattice point in FCC???

hermtm2

Hi, I am having a trouble to figure the number of lattie point in FCC structure out. My text book said simple cubic has 1 lattice point, BCC has 2 points, and FCC has 4 points. However there is no further explaination or figures. I am a kind of understand about the simple cubic structure since the atom on every corner is the lattice point.

Can you guys explain that how the lattice points in FCC and BCC are 4 and 2?

Thanks.

spf

Atoms on the sides are shared between two unit cells, so you can only count each one as 1/2 atom. Atoms on the edges are shared four unit cells, so they count as 1/4 atoms. Atoms on the corners are shared between eight unit cells, so they count as 1/8 atoms. Do the numbers add up now?

hermtm2

So, one whole atom represents for one lattice point, right?

spf

Yes. If you like, just replace "atom" by "lattice point" everywhere in my previous post.