# A Coarse-Grained Molecular Model for Simulating Self-Healing of Bitumen
## 2 Establishment of Molecular Model
### Coarse-Grained Molecular Dynamics  
The equilibration steps for the coarse-grained model are comparable to those of the all-atom one, as follows:  
1. Color the CG molecule models of each component of the bitumen separately for subsequent studies on the effect of the components upon the properties of the bitumen system. The asphaltenes are colored red, the aromatics green, the polar aromatics yellow and the saturates blue.
2. Construct a square calculation box with periodic boundary conditions, side lengths of the box are 30 nm and the initial density of the box is 0.15 g/cm\({}^{3}\), then input the CG molecular model of each component into the box in terms of the mass ratio;
3. Conduct geometric optimization (energy minimization), which should be as full as possible since the CG molecular model is larger with more particles than the all-atom one, setting the number of iterations at 40,000;
4. Relaxing the model for 2000 ps at 533 K in the NVT ensemble to reach the energy minimum conformation;  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Bead 1** & **Middle Bead** & **Bead 2** & \(\theta_{0}\) **(\({}^{\circ}\))** & **Bead 1** & **Middle Bead** & **Bead 2** & \(\theta_{0}\) **(\({}^{\circ}\))** \\ \hline C3 & C3 & C3 & 81.6 & C3 & B1 & C4a & 154 \\ C3 & C3 & C4a & 84.7 & C3 & B1 & C4b & 163.3 \\ C3 & C3 & C5a & 86 & C3 & B1 & C5b & 161.5 \\ C3 & C3 & B1 & 96.8 & C3 & B1 & B2 & 165.6 \\ C3 & C3 & B2 & 89.3 & C3 & B1 & B3 & 156.3 \\ C4a & C3 & C4a & 118.3 & C5a & B1 & B2 & 165 \\ C4a & C3 & C4b & 105.6 & C5b & B1 & B7 & 153.1 \\ C4a & C3 & B1 & 107.6 & B2 & B1 & B2 & 163.4 \\ C4a & C3 & B2 & 100.6 & B2 & B1 & B3 & 160.3 \\ C4b & C3 & C4b & 88.5 & B2 & B1 & B7 & 169.7 \\ C4b & C3 & B1 & 91.3 & B6 & B1 & B6 & 174.3 \\ C3 & C4a & C3 & 86.3 & C3 & B2 & C3 & 89.6 \\ C3 & C4a & C4a & 95.7 & C3 & B2 & C4b & 81.6 \\ C3 & C4a & B1 & 86.9 & C3 & B2 & B1 & 80.9 \\ C3 & C4a & B4 & 86.4 & C3 & B2 & B6 & 91.6 \\ C3 & C4a & N3 & 83.7 & C4a & B2 & C5a & 89.1 \\ C4a & C4a & C5a & 95.3 & C4a & B2 & B2 & 89.6 \\ C5a & C4a & B5 & 162 & C4b & B2 & B1 & 74.4 \\ B2 & C4a & B2 & 169.5 & C4b & B2 & B6 & 84.8 \\ C3 & C4b & C3 & 167.6 & C5a & B2 & B1 & 80 \\ C3 & C4b & C4b & 170.2 & C5a & B2 & B6 & 93.8 \\ C3 & C4b & B1 & 157.3 & C5a & B2 & N2 & 85.6 \\ C4b & C4b & C5a & 165.5 & C6 & B2 & B1 & 166.4 \\ C5a & C4b & C5a & 144.2 & B1 & B2 & B1 & 80.5 \\ C5a & C4b & N2 & 159.5 & B1 & B2 & B2 & 75.4 \\ C3 & C5a & C4b & 82.5 & B1 & B2 & B6 & 85.4 \\ C3 & C5a & C5a & 75.5 & B1 & B2 & N1 & 84.6 \\ C4a & C5a & C5a & 77.7 & C5a & B3 & B1 & 89.9 \\ C4a & C5a & B1 & 104.9 & C4b & B6 & B2 & 152.5 \\ C4b & C5a & C5a & 104 & B2 & B6 & B2 & 153.6 \\ C4b & C5a & B1 & 97.5 & B1 & B7 & B1 & 91 \\ C4b & C5a & N2 & 97.4 & C4b & N2 & C5a & 164 \\ C5a & C5a & C5a & 107.6 & C4b & N2 & B2 & 162.7 \\ C5a & C5a & N2 & 108.4 & C5a & N2 & C5a & 161.3 \\ B1 & C5a & B2 & 101.2 & C5a & N2 & B2 & 158.2 \\ B4 & C6 & S1 & 89.6 & C4a & S1 & C6 & 152.7 \\ C3 & B1 & C3 & 158.2 & & & & \\ \hline \end{tabular}
\end{table}
Table 7: Force field parameter \(\theta_{0}\).  
(5)  
Simulate the model for 3000 ps at 533 K and 10 atm in the NPT ensemble, then 1000 ps at 1 atm. The 10 atm run is for accelerating the compression of the model, and the 1 atm run is to achieve the desired final pressure.  
The final configuration is shown in Figure 3. The volume of the simulation is 6128.5 nm\({}^{3}\), which is about 112 times that of the all-atom molecular model.