In fact, the most eye-catching difference results from a feature that is inherited from the fullyhydrated case-the 0.01 units larger β-carbon S CH in OPLS4 (cf. Fig. ). The only qualitative differences occur at the extreme dehydration of 5 w/l; here g 3 forks only in OPLS4, and DMPC α only in CHARMM36. Few quantitative differences are also observable at 5 w/l: POPC β forks more in CHARMM36, and POPC g 1S is slightly more negative in OPLS4. But beyond these minutiae, and the perhaps slightly weaker response of OPLS4 in DMPC g 2 and g 1R , the two force fields arein good and in bad-indistinguishable in their headgroup and backbone responses to dehydration.