Given the planar nature of the membranes, the normal of the bilayer was assumed to be the z-axis. The angle between the headgroup and the tail vectors extending from the central carbon atom to the terminal atom (C5-C20, C5-C35) was calculated in a similar way. Tail splay angles were calculated with gmx gangle by selecting 1) second tail carbon atoms C9 and C22 (splay 1) and 2) terminal carbon atoms C20 and C35 (splay 2). In both cases, the same central carbon atom, i.e., C5, was selected. In addition, we computed the tail rotational autocorrelation function (ACF rot ) using a vector extending from the first carbon atom to the terminal carbon atom (C7-C20, C21-C35). The equation for calculating the autocorrelation function (ACF) of a given property f is defined as