Problem on difference in total potential energy and summation of per-atom potential energy



Hi. lammps users








I’m trying to simulate the behaviors of graphene sheets when one sheet of graphene is opening.








So, i want calculate the surface energy.








But, in this process, i hava a problem.








The total potential energy and summation of per-atom potential energy are not same in my result.








How can it be?? I’m very confused.








This is my code.



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log grap1.log



# ---------- Initialize Simulation ---------------------



clear



units metal



dimension 3



boundary p p p



newton on








# ---------- Atoms definition ---------------------



read_restart graphene-5L.restart








# ---------- Define Interatomic Potential ---------------------



pair_style airebo 3.0



pair_coeff * * CH.airebo C C



neighbor 0.2 bin



neigh_modify delay 0 every 1 check yes








#--------------Setting-------------------------------



compute eng all pe/atom



compute eatoms all reduce sum c_eng








thermo 10



thermo_style custom step lx ly lz press pxx pyy pzz pe temp








#-------------Dynamic------------------------








# variables



reset_timestep 0








#variable natoms equal count(out)



variable Epot equal pe



#variable Epot0 equal {Epot}<br><br><br><br>variable NF equal fcm(out,z)<br><br><br><br>variable zo equal xcm(out,z)<br><br><br><br>variable zb equal xcm(bottom,z)<br><br><br><br>variable nf0 equal {NF}



variable zo0 equal {zo}<br><br><br><br>variable teng equal "c_eatoms"<br><br><br><br><br><br><br><br><br><br><br><br><br><br>fix 2 all nvt temp 300 300 0.01<br><br><br><br>fix 3 bottom momentum 1 linear 1 1 1 angular<br><br><br><br>fix_modify 2 energy yes # extended Hamiltonian for NVT<br><br><br><br>fix extra out print 10 "{NF}" file nf.txt



fix disp out print 10 “{zo}" file dis.txt<br><br><br><br>#fix disp1 bottom print 10 "Displacement = {zb}” file dis1.txt



fix disp2 all print 10 “${Epot}” file pe.txt








velocity out set 0.0 0.0 20.0 sum no units box








dump 1 all atom 10 dump.gra








thermo 10



thermo_style custom step temp pe lx ly lz press c_eatoms








run 400








quit



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And, the result shows different value between total pot and summation of per-atom energy.








Step Temp PotEng Lx Ly Lz Press eatoms



0 378.36359 -15392.957 31.461894 33.534282 100 1214.9496 -15392.957







10 341.0589 -15382.87 31.461894 33.534282 100 718.54157 -15392.349








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I’m waiting your helps.








Thanks.






|

Please post a simple small example where the
difference occurs. E.g. a data file that
is read in for a single snapshot and a run 0, where the two
energies disagree. For as small a problem
as possible. Then we can look into what
is causing the difference.

Steve