Speaker
Description
We produce curved graphene hyperbolic pseudosphere surfaces in molecular dynamics (MD) simulation of a nano-scale extrusion process, in which C atoms are forced down a pseudo two-dimensional volume shaped like a hyperbolic pseudosphere. During the extrusion process the carbon atoms form pentagons, hexagons and heptagons and such a mixture is unrealistically less stable than pure graphite or diamond, by several eV/atom. During relaxation and lengthy high temperature annealing up to 0.1 microsecond (100mil. MD steps) after the extrusion process, the structure fast finds its equilibrium and polycrystalline curved graphene with a limited number of point defects is formed. The point defects cause bending of the graphene and the pseudosphere edges even more. When these free edges are removed from the simulations by attaching periodic flat graphene sheets to the pseudosphere edges, the carbon atoms assume positions with a root mean square deviation of some tenths of Å from the mathematical hyperbolic pseudosphere surface. The hyperbolic pseudospheres proved to be mechanically stable against large shearing and elongation deformations as well as against annealing at 1500 K. Our methodology is easy to use, employing the REBO2 carbon interaction potential [1] within the open source MD code LAMMPS [2]. Systems of less than 10000 atoms only scale efficiently on small numbers of cpu cores, but do require ~one week of runtime to complete 100mil. MD steps. Our method offers a practical way to create simulated stable, curved graphene surfaces with a wide variety of desired shapes. It allows for the testing in advance of the stability of graphene shapes that are to be produced experimentally.
[1] D. W. Brenner, O. A. Shenderova, J. A. Harrison, S. J. Stuart, B. Ni, S. B. Sinnott, “A second-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons”, J. Phys.: Condens. Matter 14 (2002) 783–802
[2] S. Plimpton, “Fast Parallel Algorithms for Short-Range Molecular Dynamics”, J. Comput. Phys. 117 (1995) 1
