After using change_box, how many atoms remain in you system?  to use NPT ensemble, you need large number of atoms. 

Dear Ansari,

thanks for your answer. but i didn't use NPT. I use NVT ensemble for my simulation. Is the number of atoms important in NVT or not?

Best

But you said the pressure in the system is negative or NAN. I number of atoms is not large enough, the pressure can not be calculate correctly. can you share a photo of LAMMPS log file?

i use the change_box command and after that the  created data uses for another simulation. here is my log file. any idea is highly appreceiated.

Best

dear Sa Ja

I have checked you log file. I can not understand a lot of thing, but for now:

1-   variable press equal -(c_p[1]+c_p[2]+c_p[3])/(3*vol)       ; how much is vol? you simulation volume is 28*28*70 = 54880, if vol is equal it, I think it is not true. because water molecules are only inside the CNT and vol should be CNT volume. 

2- why do you have 8 type of atoms? type 1 in Hydrogen, 2? 3? 4? 5? 6? 8 is CNT atoms?

Dear Ansari,

for pressure should i use the volume of simulation box or our system? how about the press that we write in thermo_style? how has it been calculated?

type 1: H  type 8: O . type 3 ,5 ,6 : C

1- You should consider inside volume of CNT.

2- Why do you have different types on carbon atoms in your system?

thanks

because i have two reservoirs of water and two piston before,and now i remove them.

I use these command for calculatig pressure in the manual, it says that These lines compute pressure in an input script for a 3d system. any suggestion?

thank you

could you also give me a plot (visual photo) of your system configuration before and after having reservoirs?

yes. the example of my simulation.

Can you also do this: please print the vol, c_p[1], c_p[2], and  c_p[3] and let me know what are these values?

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

excuse me for my late reply. yes it is possible. I send it.

vol, c_p[1] ,...