Basis in different types of unit cels

Physics Q&A
1

Hi,

I was wondering if the basis for e.g. a FCC would change if you would construct this for a primitive cell or a conventional cell. I would say for a primitive it’s (0,0,0) but this is clearly not the case for the conventional. Is this true?

Thanks

2

You are absolutely right. The conventional unit cell is 4x the size, so it has 4x more atoms in the basis.

3

How would I know with respect to what basis I need to work? Would this be given ?

4

Usually we ask to define lattice vectors and specify whether they should be primitive or conventional, and then ask to write down the basis corresponding to those vectors. So in other words, we give instructions that are sufficient to solve the problem, and if the formulation is ambiguous, we treat the misunderstanding in student favor.