## 2 Methodology
### Simulation Details  
As shown in Figure 1, the gas-liquid system consists of a liquid alkane in the middle and a gas on both sides, and the dimensions of the simulation cell are \(\mathrm{Lx}\)\(\times\)\(\mathrm{Ly}\)\(\times\)\(\mathrm{Lz}\) = 5 \(\times\)\(5\times\)\(30\) nm\({}^{3}\). The systems considered in this study include the binary system of CH\({}_{4}\)+n-decane, and the ternary systems of CH\({}_{4}\) + CO\({}_{2}\) + n-decane, CH\({}_{4}\) + n-hexane + n-decane, and CH\({}_{4}\) + n-decane + n-nonadecane. The simulation is performed on a mixture containing more than 10,000 atoms, where the number of alkane molecules is constant at 800, and the pressure of the system is controlled by varying the number of gas molecules introduced. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Molecular** & **Atom** & \(\sigma\)**(nm)** & \(\varepsilon_{ij}\)**(KJ\(\cdot\)mol\({}^{-1}\))** & \(q_{i}\)**(e)** & **Model** \\ \hline n-decane & C(CH\({}_{3}\)) & \(0.3910\) & \(0.8647\) & \(0\) & NERD [26] \\  & C(CH\({}_{2}\)) & \(0.3930\) & \(0.3808\) & \(0\) & TraPPE-UA [27] \\ CH\({}_{4}\) & C(CH\({}_{4}\)) & \(0.3730\) & \(1.2300\) & \(0\) & TraPPE-UA [27] \\ CO\({}_{2}\) & C & \(0.2800\) & \(0.23397\) & \(+0.6512\) & ZHU [28] \\  & O & \(0.3028\) & \(0.66824\) & \(-0.3256\) & ZHU [28] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters for non-bonded interactions. Figure 1: Gas–oil phase simulation systems: (**a**) CH\({}_{4}\) + n-decane binary mixture system, (**b**) CH\({}_{4}\) + CO\({}_{2}\) + n-decane ternary mixed system. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Stretch** & \(r_{0}\) **(nm)** & \(k_{ij}^{b}\) **(KJ-mol\({}^{-1}\)-nm\({}^{-2}\))** \\ \hline CH\({}_{x}\)-CH\({}_{y}\) & \(0.1540\) & \(80,235,028\) \\ C-O & \(0.1162\) & \(60,000\) \\ \hline
**Bend** & \(\theta_{0}\) **(°)** & \(k_{0}\) **(KJ-mol\({}^{-1}\)-rad\({}^{-2}\))** \\ \hline CH\({}_{x}\)-CH\({}_{2}\)-CH\({}_{y}\) & \(114.0\) & \(519.657\) \\ O-C-O & \(180\) & \(110\) \\ \hline
**Torsion** & \(V_{0}\) **(KJ-mol\({}^{-1}\))** & \(V_{1}\) **(KJ-mol\({}^{-1}\))** & \(V_{2}\) **(KJ-mol\({}^{-1}\))** & \(V_{3}\) **(KJ-mol\({}^{-1}\))** \\ \hline CH\({}_{x}\)-CH\({}_{2}\)-CH\({}_{2}\)-CH\({}_{y}\) & \(0\) & \(5.9038\) & \(-1.1339\) & \(13.159\) \\ \hline \hline \end{tabular} Note: x = 2 or 3, y = 2 or 3.  
\end{table} 
Table 2: Parameters for bonded interactions. The configuration snapshots were created using OVITO software (Version 2.9.0) [30]. A Nose-Hoover thermostat was used throughout the MD simulations to keep the temperature constant [31; 32]. The particle-particle-particle-mesh (PPPM) summation method was used for the long-range force electrostatic interactions, with an accuracy of 1.0 \(\times\) 10\({}^{-4}\)[33]. The cell parallel to the interface direction was 5 \(\times\) 5 nm\({}^{2}\) and the cutoff radius for non-bonding interaction forces was 2 nm (Approx.6\(\sigma\)), these values were chosen to reduce the truncation and system size effects in the interface property calculations [34; 35; 36]. The simulation time step was 1 fs. The entire simulation time comprised 10 ns of relaxation time and 30 ns of production time, with statistics at 10 ps intervals, and the IFT of the system was calculated. The IFT was calculated as Equation (9) [37]. \[\gamma==\frac{1}{2}\left[P_{zz}-\frac{\left(P_{xx}+P_{yy}\right)}{2}\right]L_{Z} \tag{9}\]  
where \(\gamma\) is the IFT, \(P_{N}(z)\) and \(P_{T}(z)\) are the normal and tangential pressures, \(P_{\alpha\alpha}\) is the amount on the diagonal of the pressure tensor, and \(L_{Z}\) is the length of the simulated system in the z-direction. The variation of the mean square displacement (MSD) with time characterizes the diffusion behavior of the atoms [38]. The expression for MSD is as follows. \[MSD(t)=\left\langle|r_{i}(t)-r_{i}(0)|^{2}\right\rangle \tag{10}\]  
where \(r_{i}(0)\) represents the position of atom \(i\) at the initial moment and \(r_{i}(t)\) represents the position of atom \(i\) at the moment \(t\).