Reducing lammps oscillation

LAMMPS LAMMPS General Discussion
1

Dear lammps user.
What are the commands and methods to reduce the oscillation after my simulation results come out? I am desperately waiting.

Sincerely.
Long

------------------------ INITIALIZATION -----------------------------------------------

units metal

atom_style full

dimension 3

boundary p p p

atom_modify map array sort 0 0.0

comm_modify vel yes

----------------- ATOMS DEFINITION ---------------------------------------------

read_data data.lammps

------------------------ FORCE FIELDS -------------------------------------------------

kspace_style pppm 1.0e-5

pair_style buck/coul/long 8.0 12.0 12.0

pair_coeff * * 0.00 0.100000 0.000000

pair_coeff 1 3 897459.51 0.420094 0.000000

pair_coeff 2 3 96327.40 0.375684 0.000000

pair_coeff 3 3 7529.17 0.985672 0.000000

neighbor 2.0 bin

neigh_modify every 1 delay 0 check yes

------------------------ INITIAL VELOCITIES -------------------------------------------

velocity all create 200 12345 mom yes rot no

------------------------- THERMALIZATION ----------------------------------------------

min_style sd

minimize 1e-8 1e-9 8000 9000

#--------------------------THERMO INFORMATION SHOWS--------------------------------------

thermo_style custom step temp etotal ke pe cella cellb cellc cellalpha cellbeta cellgamma vol press v_dipole_x v_dipole_y v_dipole_z

#--------------------------RELAXTION PROCESS---------------------------------------------

timestep 0.0004

fix 1 all npt temp 200 200 0.04 tri 1.0 1.0 0.04

thermo 2500

dump D1 all custom 500 dumps/stab1_*.txt id type x y z q

dump_modify D1 sort id element Sr Ti O

run 200000

unfix 1

undump D1

#--------------------------ELECTRIC FIELD------------------------------------------------

reset_timestep 0

timestep 0.0004

variable modE equal 1.8e-2cos((2.0PI*ceil(step/250)*250)/2500)

fix Etetra all efield 0 0 v_modE

fix 2 all npt temp 200 200 0.04 tri 1.0 1.0 0.04

fix med all ave/time 25 100 2500 v_modE file HyL.txt

thermo 2500

dump D2 all custom 500 dumps/stab2_*.txt id type x y z q

dump_modify D2 sort id element Sr Ti O

run 500000

write_restart bt_cs.rst

Graph1
Graph15332×4471 131 KB

2

Any observable in an MD simulation fluctuates. That is built-in and a consequence of the comparatively small number of atoms you simulate compared to a bulk system. As with any statistical analysis, you should get more converged results by increasing the sample size, i.e. simulate a larger system, or - if you are simulating a system in equilibrium - average over time, or both. Please refer to your favorite textbooks on Statistical Mechanics or Statistical Thermodynamics for more details. To do meaningful simulations and correct interpretation of your results, that kind of knowledge and understanding is a fundamental requirement, anyway.