It is difficult to comment on these things without knowing more details about how you compiled and run LAMMPS. Also your numbers are tricky to interpret and I don’t understand exactly what you are mean by “normalized”.
It would be better if you report:
- LAMMPS version used
- Compiler type and version
- MPI library and version
- Compiler flags
- Command lines
- System size
- Processor affinity related settings (and MPI library defaults!) and environment variables
For reliable benchmark numbers you should be running on a machine that you have exclusive access to and where there is nothing else running on. So LAMMPS should always report 100% or close to 100% CPU utilization for MPI-only and similarly higher values for OpenMP threads (but since not the entire code is run with active threads, you will not reach N_threads * 100%).
You also should note that CPU utilization is not a good measure for parallel efficiency. You can have high utilization (e.g. through busy looping) and still low parallel efficiency. So only absolute times matter.
Finally, depending on the system size, there is a limit for strong scaling, i.e. the ability to run faster with more CPUs used.