LAMMPS : Potential energy of entire system is coming almost two time as the sum of potential energy of individual atoms in the system calculated by

compute 3 all pe/atom

compute 4 all reduce sum c_3

commands.

Physically both should be equal in magnitude.

Here I am writing the input commands file.

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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

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OUTPUT of thermo_style

Step        Temp      PotEng         TotEng          c_4

1000 1996.2558 -1459674.8 -1445209.2 -748980.04

1001 1997.0884 -1459680.7 -1445209.1 -748987.39

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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 ? Can anybody help me to resolve the issue ?

Omkar