[gmx-users] Can I use RMSD increase to indicate the unfolding while the Rg remains unchanged?

[ZHANG Cheng]

I think it is a common practice to use RMSD increase to indicate the structure deformation. And in many cases, this deformation is referred as unfolding. 


But I think the RMSD increase could also come from collapse (i.e. shrinkage). So would radius of gyration (Rg) be a better descriptor for unfolding? Would unfolding always result in Rg increase? 


I often see Rg unchanged or even decreases when RMSD increases.


Thank you!