Reparameterization of the REBO-CHO potential for graphene oxide molecular dynamics simulations

The reactive empirical bond order (REBO) potential developed by Brenner et al. [Phys. Rev. B 42, 9458 (1990); J. Phys. Condens. Matter 14, 783 (2002)] for molecular dynamics (MD) simulations of hydrocarbons, and recently extended to include interactions with oxygen atoms by Ni et al. [J. Phys. Condens. Matter 16, 7261 (2004)], is modified for graphene-oxide (GO). Based on density-functional-theory (DFT) calculations, we optimized the REBO-CHO potential (in which CHO denotes carbon, hydrogen, and oxygen) to improve its ability to calculate the binding energy of an oxygen atom to graphene and the equilibrium C-O bond distances. In this work, the approach toward the optimization is based on modifying the bond order term. The modified REBO-CHO potential is applied to investigate the properties of some GO samples.

Figure 1

Top and lateral views of existing GO species from DFT calculations. (a) GO-epoxide or GO-bridgesite; (b) GO-topsite; and (c) GO-hydroxyl.

Figure 2

Static energy of GO vs distance along $z$ (left) and $x$ (right) directions for the C–O bonds in GO-epoxide system. The calculated frequencies of C–O oscillations with both REBO-CHO and DFT are shown in red and green, respectively. Dots represent MD calculations, and the blue line is the best parabolic fitting. The inset shows the local structure and the local system of coordinates.

Figure 3

Static energy of GO vs distance along the $z$ (left) direction for the C–O bonds in the GO-hydroxyl system. The calculated frequencies of C–O oscillations with both REBO-CHO and DFT are shown in red and green, respectively. Dots represent MD calculations, and the blue line is the best parabolic fitting. The inset shows the local structure and the local system of coordinates.

Figure 4

A snapshot of a GO-epoxide structure after 90 ps of a MD simulation at 3000 K. O${}_2$ molecules, marked with yellow circles, form due to desorption of oxygen atoms. The initial structure used for these simulations was the GO-topsite, shown in Fig. 1b.

Figure 5

Static energy of graphene and O${}_2$ molecule vs distance between them for original (black circle) and modified (gray square) parametrization of REBO-CHO.

Figure 6

Structure and bond distances in angstroms of the C${}_4$H${}_{10}$O molecule as relaxed by original (left) and modified (right) REBO-CHO.