[lammps-users] fix nvt/sphere

Dear all, do you know why the fix nvt/sphere command in my input file cannot update the positions, velocities and angular velocities of the grain correctly? Thank you very much!

This is my input file:

units si
dimension 3
atom_style granular
boundary p p p
newton off
read_data chain1d.granule
pair_style gran/hertz/history 20000000.0 0 0000.0 0 0 0
pair_coeff * *
communicate single vel yes
neighbor 1 bin
neigh_modify delay 0
timestep 1.0e-8
fix 1 all nvt/sphere 300.0 300.0 100.0
compute RKE all erotate/sphere
thermo_style custom step atoms ke c_RKE vol
thermo 1000000
dump coor all custom 1000000 dump.granule id type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius
run 10000000

This is the file of chain1D.granule:

LAMMPS data file for 1D granular gas

2 atoms

1 atom types

-10000.0 10000.0 xlo xhi
-1.0 1.0 ylo yhi
-1.0 1.0 zlo zhi

Atoms

1 1 0.1 7900 0 0 0
2 1 0.1 7900 0 -0.15 0

Velocities

1 0 -5 0 0 0 0
2 0 0 0 0 0 0

This is the output:

Step Atoms KinEng RKE Volume
0 2 51.705379 0 80000
1000000 2 0 0 80000
2000000 2 0 0 80000
3000000 2 0 0 80000
4000000 2 0 0 80000
5000000 2 0 0 80000
6000000 2 0 0 80000
7000000 2 0 0 80000
8000000 2 0 0 80000
9000000 2 0 0 80000
10000000 2 0 0 80000
You can see that the kinetic energy becomes 0 in the very beginning.

Granular models don't typically have a temperature, per se,
since the pair interactions are dissipative. So trying to
thermostat them with nvt is not a good idea.

Steve

2010/1/14 unica111 <[email protected]>:

Dear Steve, thank you for your advice. So do you mean fix nvt/sphere can not act on the granular models in the LAMMPS source code?

在2010-01-14 23:35:02,"Steve Plimpton" <[email protected]> 写道:
>Granular models don't typically have a temperature, per se,
>since the pair interactions are dissipative.  So trying to
>thermostat them with nvt is not a good idea.
>
>Steve
>
>2010/1/14 unica111 <[email protected]>:
>> Dear all, do you know why the fix nvt/sphere command in my input file cannot
>> update the positions, velocities and angular velocities of the grain
>> correctly? Thank you very much!
>> This is my input file:
>> units si
>> dimension 3
>> atom_style granular
>> boundary p p p
>> newton off
>> read_data chain1d.granule
>> pair_style gran/hertz/history 20000000.0 0 0000.0 0 0 0
>> pair_coeff * *
>> communicate single vel yes
>> neighbor 1 bin
>> neigh_modify delay 0
>> timestep 1.0e-8
>> fix 1 all nvt/sphere 300.0 300.0 100.0
>> compute RKE all erotate/sphere
>> thermo_style custom step atoms ke c_RKE vol
>> thermo 1000000
>> dump coor all custom 1000000 dump.granule id type x y z ix iy iz vx vy vz fx
>> fy fz omegax omegay omegaz radius
>> run 10000000
>> This is the file of chain1D.granule:
>> LAMMPS data file for 1D granular gas
>> 2     atoms
>> 1     atom types
>> -10000.0 10000.0 xlo xhi
>> -1.0 1.0 ylo yhi
>> -1.0 1.0 zlo zhi
>> Atoms
>>            1           1        0.1     7900        0        0        0
>>            2           1        0.1     7900        0        -0.15    0
>>  Velocities
>>            1        0        -5        0        0        0        0
>>            2        0        0        0        0        0        0
>> This is the output:
>> Step Atoms KinEng RKE Volume
>>        0        2    51.705379            0        80000
>>  1000000        2            0            0        80000
>>  2000000        2            0            0        80000
>>  3000000        2            0            0        80000
>>  4000000        2            0            0        80000
>>  5000000        2            0            0        80000
>>  6000000        2            0            0        80000
>>  7000000        2            0            0        80000
>>  8000000        2            0            0        80000
>>  9000000        2            0            0        80000
>> 10000000        2            0            0        80000
>> You can see that the kinetic energy becomes 0 in the very beginning.
>>
>>
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I mean it doesn't typically make sense to thermostat granular
particles, however you do it (Nose/Hoover, etc). The dissipative
terms are taking out energy and the thermostat will be trying to put
it back in, and that is a recipe for bad dynamics.

Steve

2010/1/14 unica111 <[email protected]>: