Abstract
Large samples of experimentally produced graphene are polycrystalline. For the study of this material, it helps to have realistic computer samples that are also polycrystalline. A common approach to produce such samples in computer simulations is based on the method of Wooten, Winer, and Weaire, originally introduced for the simulation of amorphous silicon. We introduce an early rejection variation of their method, applied to graphene, which exploits the local nature of the structural changes to achieve a significant speed-up in the relaxation of the material, without compromising the dynamics. We test it on a 3200 atoms sample, obtaining a speed-up between one and two orders of magnitude. We also introduce a further variation called early decision specifically for relaxing large samples even faster, and we test it on two samples of 10,024 and 20,000 atoms, obtaining a further speed-up of an order of magnitude. Furthermore, we provide a graphical manipulation tool to remove unwanted artifacts in a sample, such as bond crossings.
Highlights
Graphene is a crystal of carbon atoms that form a three-coordinated honeycomb lattice.It is a material with a large set of exotic properties, both mechanical and electronic, and it has the particularity of being a two-dimensional crystal embedded in a three-dimensional space [1,2,3,4,5,6,7,8]
As an alternative for such cases, the early decision approach: the decision on whether to reject or accept a bond transposition after the local relaxation is treated as final, without having to perform a global relaxation to accept it
We introduced two techniques that, through local relaxation, can estimate the success of bond transpositions reducing or eliminating the need for relaxing the entire sample, which is extremely time-consuming. Both techniques significantly reduce the computational time required per accepted bond transposition: the early rejection method by immediately rejecting, without a global relaxation, hopeless attempts; the early decision method avoids global relaxations entirely, relying on the estimate of the energy of the relaxed sample
Summary
Graphene is a crystal of carbon atoms that form a three-coordinated honeycomb lattice.It is a material with a large set of exotic properties, both mechanical and electronic, and it has the particularity of being a two-dimensional crystal embedded in a three-dimensional space [1,2,3,4,5,6,7,8]. Large samples experimentally produced are usually polycrystalline, containing intrinsic [9,10,11], as well as extrinsic [12] lattice defects These defects warrant a thorough study as they both have a significant detrimental effect on the properties expected from pristine graphene [13,14], and they can cause new effects that are otherwise absent [15,16,17,18]. Structural defects are both prominent and common in graphene [19], as they can host lattice defects due to the flexibility of the carbon atoms in hybridization Such defects can be frozen in the sample during the annealing process and have been experimentally observed [20,21,22]. Their controlled production in graphene has been explored [23]
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