Dear All,
I am using LAMMPS (14 Feb 2014) and have some questions about shock simulation:
1.To generate planar shock waves in NEMD simulations, we usually use fix wall/piston command to drive a piston at a specific particle velocity onto a stationary simulation cell. According to manual, we can set the position of the piston via keyword ‘pos’ .Now,I have a question:
‘fix walls all wall/piston zlo pos 5.0 0.0 0.0 vel 0.0 0.0 10.0 units box’, we know the z coordinate at which the piston begins is 5.Does it mean the thickness of the piston at z coordinate is 5? Are the atoms in 0~5 coordinate rigid atoms?

2.Also, I set the pos as 0,such as ‘fix walls all wall/piston zlo pos 0.0 0.0 0.0 vel 0.0 0.0 10.0 units box’, it seems there isn’t any significant difference about the result of shock simulation. I wonder whether there are some other differences between these two commands?

3.Another way to generate shock wave is to impacta simulation cell onto a piston at a specified particle velocity.To construct the piston, we can use fix wall/reflect via ‘fix walls all wall/reflect zlo 0.0’
Also,we can use ‘fix walls all wall/piston zlo pos 0.0 0.0 0.0 vel 0.0 0.0 0.0’
Can these two command reach the same result when reflecting atoms?

4.fix wall/piston and fix wall/reflect usually are used in conjuction with fix nve. Can these setting keep the energy in the shock hugoniot state like fix msst or fix nphug?

Thank you very much for your answer
Best regards,