fix rigid/nvt

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1

dear all
I have a simple system with data file attached below and i made it rigid with the below code and i ran it for 200000 femtosecond in order to relax it but it keeps moving and rotating and never reaches the desired temperature which is 310 k.
i would appreciate if someone help me.
sincerely
shahriar dadras
my code:
units real
boundary p p p
atom_style full
pair_style buck/coul/cut 10.0 8.0
read_data buckdata.data group nanoparticle
set type 1 charge 1.68 # nanoparticle1 F
set type 2 charge 1.6 # nanoparticle1 Fe
set type 3 charge -1.22 # nanoparticle2 O

pair_coeff 1 3 25421.94 0.3299 0 10.0
pair_coeff 2 3 18730 0.3399 0 10.0
pair_coeff 3 3 524950 0.149 15 10.0
pair_coeff 1 1 0 1 0 10.0
pair_coeff 2 2 0 1 0 10.0
pair_coeff 1 2 0 1 0 10.0

velocity all create 310.0 12345678 dist uniform rot yes

special_bonds charmm
thermo 1
thermo_style multi
timestep 1.0

dump 1 all atom 10 membrane.lammpstrj

minimize 0.00001 0.0001 1000000 10000000

fix rigid nanoparticle rigid/nvt molecule temp 310 310 20
reset_timestep 0
dump 2 all atom 100 membrane2.lammpstrj
compute sss nanoparticle temp
compute fff nanoparticle temp/com
thermo 10
thermo_style custom step temp press etotal pe ke c_fff
run 200000

buckdata.data (16.6 KB)

2

there is not much to help. this is not a LAMMPS problem, but a problem of understanding statistical mechanics.

since your system has only this one rigid object, it makes very little sense to set and compute a temperature.
you only have 6 degrees of freedom (3x translation, 3x rotation) and since there is nothing else in your system,
they have no meaning. the translation of the entire system is not considered anyway.

and because what you want to get has no meaning for this setup, there is nothing that needs to be changed.
in fact, doing an MD for such a system has no meaning.

axel.