## 2 Molecular Dynamics Simulations
### Asphalt Molecular Structure Construction  
Asphalt is often characterized chemically by its hydrocarbon class composition, e.g., three main constituent species including asphaltene, naphthene aromatics and saturates. The three-fraction asphalt model was employed to establish the molecular structure following [PERSON] and Greenfield [25], where three different types of molecules are used to represent the corresponding constituent species, and the three are then formed together to create an asphalt-like ensemble of molecules. In this model, 1,7-dimethylnaphthene was used to represent naphthene aromatics, and n-C\({}_{22}\) (n-doccosane) molecules were used to represent saturates, with the mass fraction of asphaltenes, naphthene aromatics, and saturates being approximately 20:60:20, respectively.  
The condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field was used for our simulation, considering that this force field could accurately describe the inorganic material properties. The initial molecular structure was constructed by using the commercial molecular computation software Material Studio 7.0 (BIOVIA Company, San Diego, CA, USA). The construction function in amorphous cell tools of Material Studio was used to construct the representative volume element in asphalt binder. The target density of the final configurations was set to 1 g/cm\({}^{3}\). Table 1 shows the detailed configuration of the asphalt-like ensemble. Figure 1 shows the constructed molecular structure, where the edge length (A) of the lattice is 50.9 \(\times\) 50.9 \(\times\) 50.9. The atoms in each molecule in the asphalt-like amorphous cell were then subjected to conjugate gradient energy minimization within 10,000 fs.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Molecular Components** & **Asphaltene** & **1,7-Dimethylnaphalene** & **n-Doccosane** \\ \hline Number & 18 & 306 & 49 \\ Approximate Mass ratio & 20 & 60 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Configuration of the asphalt-like ensemble.  
Our molecular dynamics simulation was split into two parts: constructing the model in Materials Studio due to convenience, and applying the loading conditions in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software. After construction of the asphalt molecular model in Material Studio, it was exported in a PDB-format file and imported into the VMD (Visual Molecular Dynamics) software (University of Illinois at Urbana-Champaign, Urbana-Champaign, IL, USA). By using the \"Topo writelammpsdata asphalt.data full\" command, the asphalt data file can be read by the LAMMPS software.  
The following potential function was used in our LAMMPS simulation for convenience:  
\[E=\varepsilon\bigg{[}2\Big{(}\frac{\sigma}{r}\Big{)}^{9}-3\Big{(}\frac{\sigma }{r}\Big{)}^{6}\bigg{]},\ r<r_{c} \tag{1}\]  
where \(E\) is the potential, \(\varepsilon\) is the depth of a potential well that reflects the attraction between two atoms, \(\sigma\) is the distance between atoms when the action potential is equal to 0, \(r\) is the distance between two atoms, and \(r_{c}\) is the cutoff.