I have spent hours on finding the primitive cells of honeycomb lattice of graphene. Based on the definition of graphene from most of solid state physics books, as I quoted from Wikipedia, and in which P.K. Misra, Physics of Condensed Matter book agreed,
a primitive cell is a minimum volume cell (a unit cell) corresponding to a single lattice point of a structure with discrete translational symmetry.
What I understand is that in the primitive cell we define, must contain single lattice point. But, what I found from all articles explaining graphene, the cell they defined is a unit cell which contain two lattice point, as I attached below (taken from here),
Isn't that a non-primitive unit cell? Some articles just mentioned it as unit cell, but some others claiming that it is the primitive cell of graphene. And me myself, try to find the primitive cells of graphene for hours, and still no result.
So, is my understanding of primitive cells wrong? Or, I just hadn't found the primitive cell yet?
Thanks for the help.