Structural Transitions in A Crystalline Bilayer : The Case of Lennard   Jones and Gaussian Core Models
  We study structural transitions in a system of interacting particles arranged as a crystalline bilayer, as a function of the density $\rho$ and the distance $d$ between the layers. As $d$ is decreased a sequence of transitions involving triangular, rhombic, square and centered rectangular lattices is observed. The sequence of phases and the order of transitions depends on the nature of interactions. 
Tamoghna Das, Surajit Sengupta, Subhasis Sinha