relax the graphene

[jaco]

Dear Sir,
     I have one simple question on the relaxation of the graphene. for example, I build a graphene nanoribbon in the new builder, and try to optimize it. should i make the x, y, z cell constrained or only the z cell are not constrained?
     I found that by minishing the max stree, z can be not changed. is it right?

[zh]

If the graphene ribbon is  placed in the xy plane and the periodic direction is along the x direction, you should constrain the  y and z  direction of cell. That's to say, the directions with vacuum layer should be constrained.

[jaco]

Thanks for your kindly reply!!
I am not sure what you mean, as you say, if the periodic direction is along the x direction, i think the y and z direction should to be constrained, is that your means? so what if for the graphene sheet?

[zh]

I have corrected a typo in my previous reply.

For a graphene sheet, only the z direction of cell is constrained in the cell optimization.

[jaco]

Got it!!!!
Thanks a lot Dr. zh