I use resd to restrain distance between two atoms (R) not go beyond a certain value (A1) and it works well. For some unknown reason, the MD (using openmm) ignores the image command from charmm. As a result, sometimes the simulation stops due to R jumps to a huge number. I am wondering if it is possible to set up restraint this way: include the restraint only when A1
My current resd is:
resd kval 10.0 rval 9.06 positive ival 1 -
     1.0 DNAA 17 N2  DNAA 16 O2 -
     1.0 DNAA 17 N1  DNAA 16 N3 -
     1.0 DNAA 17 O6  DNAA 16 N4

So the restraint works when R>9.06. Is it possible to make it working for 10>R>9.06?

Thank you.