(A) Work done along the forward (red) and reverse (green) pulling paths. For forward paths, the work value, , is what is done to the system when the center of WA→B(z), is what is done to the system when the center of mass of methane is pulled from zA = −14.6Å to z . For reverse paths, the work value, WB→A(z), is what is done to the system when the center of mass of methane is pulled from ZB = 15.4Å to z . The pulling speed is 0.05Å / ps . The pulling is clearly irreversible because WA→B(zB)+WB→A(zA) ≠ 0. (B) The interval (−15Å,15Å) is divided into 30 equal sub-intervals of 1Å each. Over each sub-interval, five forward and five reverse pulling paths are sampled. Work measurements are done along the forward paths (red) and along the reverse paths (green) in each sub-interval.