Hi Animesh, 

I am not sure whether I understood your question correctly. What I guessed, you want a hybrid structure wherein a single unit cell there will be Cu atoms on top of the graphene sheet. 

First of all, we have to acknowledge the difference in the unit cell of these two materials. Let's start with Cu-bcc and graphene's honeycomb structure.  We need to find a plane in Cu structure where it will be more closer to honeycomb. Cu plane is within 2% lattice constant mismatch of graphene's structure if you adjust the axis properly. Going back to your question. Let's set graphene's zigzag edge towards x-axis, and Cu plane aligned to the z-axis. Take three layers of Cu atoms. You will find a unit cell of 5 atoms: 2 from graphene, 3 for Cu. And this will be your new unit cell with a new lattice constant. However, it will follow honeycomb structure. in XY plane real space lattice vectors will be same as graphene crystal. Only you have to modify vectors along z-axis because of this modified height. The third vector depends on how you want to repeat unit cell in that direction. Which solely depends on what you want, a slab or a bulk. 

If you could elaborate on your question with few more specific then I will be able to explain details on what should be your unit cell. You can check out few figures from one of my recent work in the same line to get an idea of building a unit cell of Cu-Graphene hybrid structure.  

http://ecst.ecsdl.org/content/75/13/49.short

Thanks. 

 Hi K M Mohsin, 

Thanks for valuable reply. Actually i want to do hyper velocity impact of cu clusters on graphene sheet sothat graphene sheet will deform or break. My target is to develop a unit cell contain of cu clusters on the top of graphene sheet. Then I shall give some hyper velocity  on cu clusters sothat  all clusters will move towards the graphene sheet to hit. Basically I want to do Impact analysis of cu clusters on graphane sheet.

Hi K M Mohsin,

can you give an example of a single unit cell with atoms coordination ?