Peierls and Landau predicted that 2D crystals can't be stable: http://physics.stackexchange.com/questions/110079/why-a-mono-atomic-crystal-layer-2d-cant-be-stab

Peierls and Landau predicted that 2D crystals can't be stable: http://physics.stackexchange.com/questions/110079/why-a-mono-atomic-crystal-layer-2d-cant-be-stable http://physics.stackexchange.com/questions/110079/why-a-mono... Either they made assumptions that don't hold, or graphene actually isn't "stable" as such but is stable enough in reality. I don't know much of the history of quantum chemistry simulations of graphene, but I'm fairly sure they existed beforehand and the experiments were a nice confirmation. Quite often it's possible to simulate things which are thermodynamically impractical, with things like an incomplete thermodynamic sampling in MD, or small periodic cell sizes artificially stabilising systems.