Hi Omakar, LAMMPS mailing list is the best place to ask such questions. I think I saw your post. Just checked the issue you have raised here. It is clearly mentioned in lammps manual. Use following commands and you will get exactly same result you r expecting.

compute peratom all pe/atom

compute pe all reduce sum c_peratom

thermo_style custom step temp etotal press pe c_pe

Hope it helps. 

Thanks you Dr Tiwari for your kind suggestions. But as you have already understand my problem so I am asking you again because if I go for LAMMPS mailing list I have to again explain everything. If it is possible from your side then please answer. From next time I will opt for LAMMPS mailing list.

Here I am writing the out put from the commands

fix 1 all nve

fix 2 all temp/rescale 20 2000.0 2000.0 10.0 1.0

timestep 1.0

thermo 1

run 1000

unfix 2

compute 3 all pe/atom

compute 4 all reduce sum c_3

thermo_style custom step temp pe etotal c_4

dump 20 all custom 10 Trajectory_nve_2000 id xu yu zu vx vy vz c_3

run 1000

OUTPUT of thermo_style

Step Temp PotEng TotEng 4

1000 1996.2558 -1459674.8 -1445209.2 -748980.04

1001 1997.0884 -1459680.7 -1445209.1 -748987.39

Now just see the 3rd and the last column of the output. The 3rd column is the PE of entire system and the last column is the sum of the PE of individual atoms. These two quantity should be equal but they differs by a multiplicative factor of approximately two. I don't understand why ?

Omkar

Hi Omkar.

What units are you using? What pair style? Can you post your input file that generated the data yous how?

Please find attached a simple Ni simulation at 300 K where I am printing out the PE and PE/atom summed using your script and they match exactly!!:

Step Temp PotEng TotEng 4

0 1000 -2225 -2160.4992 -2225

25 740.39983 -2173.0586 -2125.3022 -2173.0586

50 1018.4371 -2153.2661 -2087.5761 -2153.2661

75 819.25385 -2131.3536 -2078.5111 -2131.3536

100 1000 -2147.9765 -2083.4757 -2147.9765

125 1007.3197 -2147.5365 -2082.5635 -2147.5365

150 1072.8012 -2157.7579 -2088.5614 -2157.7579

175 984.674 -2158.6458 -2095.1335 -2158.6458

I'm using lammps-1Feb14 version.

...

The whole input file.

units real

atom_style full

read_data inp_nve.xyz

kspace_style ewald/n 0.00001

kspace_modify gewald 0.24287

pair_style buck/coul/long 11.0 11.0

pair_coeff * * 0.0 1.0 0.0

pair_coeff  1  4 

pair_coeff 2   4

pair_coeff 3   4

pair_coeff 4   4

fix 1 all nve

fix 2 all temp/rescale 20 2000.0 2000.0 10.0 1.0

timestep 1.0

thermo 1

run 1000

unfix 2

compute 3 all pe/atom

compute 4 all reduce sum c_3

thermo_style custom step temp pe etotal c_4

dump 20 all custom 10 Trajectory_nve_2000 id xu yu zu vx vy vz c_3

run 1000

Hello Sir

Can you give me the input file that you have used ?

Dear Omkar,

I saw your email on LAMMPS mailing list. Maybe you should post your whole input file there, since there is no information about pair style etc. in your previous email. Maybe people there can give you more help.