Here, P L = 1/2 ⇥ (P xx + P yy ), and P xx = P yy due to symmetry, and the length of the simulation box in the direction normal to the interface is L z . The surface tension values were extracted with gmx energy, and the standard error was obtained from block averaging performed by gmx analyze. The last 9.9 ns of the 10 ns-long simulations were used for analysis.