## 2 Calculation Model and Method
### Model and Method Verification  
In order to verify the correctness of the above model and method, referring to the existing studies [30; 31], The model of pure copper (2.8952 nm \(\times\) 2.8952 nm \(\times\) 7.238 nm) and graphene/copper composite (6.506 nm \(\times\) 5.061 nm \(\times\) 5.061 nm) with the same size as the literature was established and the molecular dynamics simulation was carried out under the same conditions. Subsequently, the results of the simulation were plotted as tensile stress-strain curves, as shown in Figure 2.  
According to the curve shown in Figure 2, the curve in the straight line stage in the image is fitted, and the ultimate strain and elastic modulus of the pure copper and composite materials of the corresponding size are obtained and summarized with the literature data in Table 1.  
In order to ensure the accuracy of the model and simulation methods, in addition to keeping the model size and simulation conditions consistent with those in the literature, this section also simulated the mechanical properties of pure copper and graphene/copper matrix composites, respectively. As can be seen from Figure 1 and Table 1, the mechanical  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Pure Copper**} & \multicolumn{2}{c}{**Graphene/Copper Composites**} \\ \hline
**Parameter** & **Ultimate Strain** & **Modulus of Elasticity/GPa** & **Ultimate Strain** & **Modulus of Elasticity/GPa** \\ \hline Textual data & 0.0858 & 87.65 & 0.13 & 215.88 \\ Literature data & 0.0825 & 84.049 & 0.127 & 210.2 \\ \hline Error & 4.1\% & 4.3\% & 2.6\% & 2.7\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Model and method validation data.  
Figure 2: Tensile stress–strain curves of copper (Cu) and graphene–copper composites (Cu/Gr).  
properties of graphene/copper matrix composites are significantly better than that of pure copper. In Table 1, \"Textual data\" is the data we obtain through modeling calculations, \"Literature data\" is the calculated results of authors in references, and \"Error\" refers to the percentage difference between the above two data, which is used to describe the size of the difference. It is obvious from the table that both copper and the modulus of composite materials are tested with very close data (ultimate strain and modulus of elasticity). Especially for composite materials, the error of both data is less than 3%. Generally speaking, when the error is less than 5%, the error can be considered to be minimal or no error. Therefore, the molecular dynamics method used in this paper has been verified.  
As the most important reinforcement in the graphene/copper matrix composites, it is necessary to verify the graphene tensile, so the graphene tensile simulation was conducted in both directions. The stress-strain curve of the perfect graphene is shown in Figure 3.  
According to the curve shown in Figure 3, the curve at the stage of 0-0.04 tensile strain was fitted, and the average value was taken to show that the elastic modulus of defect-free graphene was about 1.082 TPa, which was very close to the 1.05 TPa [32] calculated by first principles and 1.0 TPa [33] measured by nanoindentation test.  
Through the above simulation verification of copper, graphene, and graphene/copper matrix composites, the data obtained are basically consistent with previous data, and the simulation method has been well verified.