# [lammps-users] in lj units damping constants

Dear Lammps users,

I have the following input script.
I will run the input script each one separately for the temperature T=1.0, T=1.2,T=1.4,T=1.6, …T=4.0(N=1024 particles and Pressure=8).

For three lines the following (in lj units):
1-fix 1 all npt/asphere 2.0 2.0 0.5 xyz 0.0 8.0 0.5
2-fix 2 all npt/asphere 2.0 2.0 0.5 xyz 8.0 8.0 0.5
3-neighbor 0.3 bin
are T damp, P damp and neighbor values convenient?
What would you recommend?

input script:

units lj
atom_style ellipsoid

lattice sc 0.01
region box block 0 8 0 8 0 16
create_box 1 box
create_atoms 1 box
set group all quat/random 18238

mass 1 1.0
shape 1 1 1 3

compute rot all temp/asphere
group spheroid type 1
variable dof equal count(spheroid)+2
compute_modify rot extra \${dof}

velocity all create 2.0 87287 loop geom

pair_style gayberne 1.0 3.0 1.0 4.0
pair_coeff 1 1 1.0 1.0 1.0 1.0 0.2 1.0 1.0 0.2
neighbor 0.3 bin

timestep 0.002
thermo_style custom step temp etotal vol epair press pe
thermo 100

fix 1 all npt/asphere 2.0 2.0 0.5 xyz 0.0 8.0 0.5
compute_modify 1_temp extra \${dof}
run 100000
unfix 1

fix 2 all npt/asphere 2.0 2.0 0.5 xyz 8.0 8.0 0.5
compute_modify 2_temp extra \${dof}
run 100000

I usually make the Pdamp constant about 10x larger
than the Tdamp, and your Tdamp is fine - it's 100
timesteps if your dt = 0.005.

Steve

2009/9/9 ahmet yıldırım <[email protected]...>:

I am sorry, I don’t understand that you last said "it’s 100 timesteps if your dt = 0.005".

İn addition, is the neighbor value- 0.3 bin convenient for ellipsoidal particles in lj units?

09 Eylül 2009 17:45 tarihinde Steve Plimpton <[email protected]> yazdı:

The damping constants in your input script
were 0.5, the (default) timestep for LJ is 0.005,
so your damping is 100x the timestep.

0.3 for the neighbor skin should be OK in LJ units

Steve

2009/9/9 ahmet yıldırım <[email protected]...>:

can I do neighbor 0.8 bin in lj units?

10 Eylül 2009 17:19 tarihinde Steve Plimpton <[email protected]> yazdı:

You can use any skin size you want. You'll just
run slower if it's too big.

Steve

2009/9/10 ahmet yıldırım <[email protected]...>: