IWCN 2021: Recursive Open Boundary and Interfaces Method for Material Property Predictions

By James Charles1; Sabre Kais2; Tillmann Christoph Kubis1

1. Electrical and Computer Engineering, Purdue University, West Lafayette, IN 2. Department of Chemistry, Purdue University, West Lafayette, IN

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Simulations are essential to accelerate the discovery of new materials and to gain full understanding of known ones. Although hard to realize experimentally, periodic boundary conditions are omnipresent in material simulations. We introduce ROBIN (recursive open boundary and interfaces) [1], the first method allowing open boundary conditions in material and interface modeling. The computational costs are limited to solving quantum properties in a focus area which allows explicitly discretizing millions of atoms in real space and to consider virtually any type of environment (be it periodic, regular, or random). Figure 1 verifies the local density of states resulting of an all-real space ROBIN calculation of pristine graphene against analytical results. The impact of the periodicity assumption is assessed in detail with silicon dopants in graphene. Graphene was confirmed to produce a band gap with periodic substitution of 3% carbon with silicon in agreement with published periodic boundary condition calculations [2]. Instead, 3% randomly distributed silicon in graphene only shifts the energy spectrum. The predicted shift agrees quantitatively with published experimental data [2]. The shift is a linear function of the Si concentration (see Fig. 3) in agreement with the small linear response a few-percent Si perturbation should yield.

The ROBIN method allows to consider the interface between graphene alloyed with 3% randomly and 3% periodically distributed Si. Figure 4 shows the significant density of states difference these only stoichiometrically identical systems show.

In summary, we show that assuming periodicity elevates a small perturbation of a periodic cell into a strong impact on the material property prediction. Periodic boundary conditions can be applied on truly periodic systems only. More general systems should apply an open boundary method for reliable predictions.

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  1. [1] Charles J. et al., ACS Materials Lett. 2, 247 (2020)
  2. Zhang, S. J. et al., Nanoscale 8, 226 (2015)

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Researchers should cite this work as follows:

  • James Charles, Sabre Kais, Tillmann Christoph Kubis (2021), "IWCN 2021: Recursive Open Boundary and Interfaces Method for Material Property Predictions,"

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