Graphene on diamond

Hello,

I want to put a layer of graphene on top of a diamond(111) surface. However, the graphene layer and the surface do not have the same crystal parameters and if I try to adjust the parameters to i) the diamond surface, ii) the graphene layer, or, iii) an average value, the model will be severly distorted.

I have looked in the help-files but I only found examples for layers that have the same parameters as the substrate.

Anyone who can help me?