error: shake clusters are clusted

When I used the united-atom force field which methyl and methylene groups are considered as one center.but I used the fix shake to constranit the C-C bond, it also shows the error shake clusters are clusted.How should I do to fix the C-C
Eagerly waiting for the reply, and thank you very much!

   Sincerely yours
   Sneaker Bai

The fix shake doc page explains the restrictions on how it can be used, i.e.

what it can constrain. There is no current capability in LAMMPS to constrain

all the C-C backbone bonds of a long-chain polymer.

Steve

thanks for your reply!