Dear teacher,thanks again for your help.I have read your reply.But also have some questions.How to add one thermal atom of type 2 to each type 1 atom, attached by a spring. I’ve already used the command of fix spring/self .However, I did not get the desired results, and I judged this command was unreasonable. Which command can be implemented in the LAMMPS. According to my own understanding, I drew a picture.See Fig1.



Create 2 atoms on top of each other, with a harmonic bond
between them (defined in the data file). Also see the

bond_style harmonic command. Make the equilibrium
bond length = 0. One of the 2 atoms (type 1) can be
frozen. The other (type 2) will oscillate around it.