Here L z is the length of the simulation box in the direction perpendicular to the liquidliquid interface, assumed to be the z-direction and the outer factor '2' derives from the fact that in periodic boundary conditions there are two interfaces. In a bulk region all three components of the pressure tensor become equal to each other and equal to the bulk pressure, P xx = P yy = P zz = p. A non-zero value for γ 12 (which must be positive) results