Dear charmm User,

recently I have started to look into Umbrella Sampling for the investigation of proton transfer reactions. For "short" proton transfer steps, e.g. between two neighboring water molecules, the rxncor module seemed to be straightforward to define some reaction coordinate like RC=d(Donor,Proton)-d(Acceptor,Proton).

For "longer" Proton trasfer steps, e.g. along a water wire, however, I would like to use some more advaced RC as for example defined by Q. Cui et al (J Phys Chem A. 2006). This RC, however, includes for example expnential functions. Therefore, I wanted to ask if there is the possibility to include such expressions in RCs in charmm and how to do that (or where to look for).

Thanks in Advance.