Hi Tobias,
nn2 is only valid for the same type of elements (meam_setup_done.F). By initializing nn2_meam(:,:)=1 you are also initializing nn2 for different type of elements. I think you can initialize nn2_meam to 1 corresponding to (1,1) or (2,2) and keep (1,2) or (2,1)=0 and see if it works.
Regards,
Rutuparna