I understand that i can use respa for implementing multi-scale timestep in evaluating bond, angle etc energies. However what i am trying to do is having different timesteps on different set of bonds and angles. Like bond style ‘a’ ‘b’ and ‘c’ has dt = ‘t1’ and ‘d’ ‘e’ ‘f’ has dt = ‘t2’. Is there a way to do it ? The faster set of atoms has no bonding connection to the slower set of atoms and hence i was wondering if playing with fix and unfix with a loop construct can give me the advantage of having bigger timestep on slower atoms. I appreciate any suggestion to this.