Yes, 8 processor takes less time compared to 1 processor but for a system this small, my simulation rate is very slow. I do not have access to GPU processing right now. 

Any suggestion for this CPU processing to make is speed up?

You're right, 25 timesteps per second (in your best case, 8 processors) is quite slow.

As you can see, more than 80% of the simulation time is spent calculating Kspace, that is, FFT for the long electrostatic interactions.

You can start by optimizing these settings in your configuration file.

How about running the simulation in single precision? Is that acceptable? There would be speed increase there too.

@Fernando, thank for replying but I could'nt follow. I did run simulation on a single processor. Speed decreased with 1 processor as shown in attached image. (or did you mean something else? )

What optimizations could you suggest regarding Kspace  ?

Yes, you ran in 1, 4 and 8 processors. 8 processors being the fastest, which is an expected result when there is no communication overhead.

What I meant by optimizing Kspace is to study LAMMPS documentation and check which parameters can you modify to improve electrostatic force calculations speed.

In line with Fernando's suggestion, if you check the lammps documentation on KSPACE package you will see that FFT is necessary for performance. Is your lammps built with FFT package? That would have a direct impact on performance.

http://lammps.sandia.gov/doc/kspace_style.html

Also you should check for the accuracy parameter. If too tight, then the simulation will be time consuming.

Finally, through kspace_modify command you might be able to make further adjustments.

http://lammps.sandia.gov/doc/kspace_modify.html

Cheers!

it is very expensive to solve long-range interaction. there are some solver in LAMMPS, e.g, ppm is faster than ewald. generally speaking, high precision means time-consming. Choose the suitable one for your system.