Dear lammps-users and developers
The simulation box has three groups: low group, flow group and upper group as followed. The all group are in NVE ensemble.
The velocity command is used to make the upper group have the stream velocity v=2.0 along the x direction. However, The stream velocity of upper group decreased gradually.
step velocity(upper group)
3000 0.893662
4000 0.851187
5000 0.824726
6000 0.80896
7000 0.792684
8000 0.770081
9000 0.748362
10000 0.732631
…
IN script:
dimension 3
boundary p f p
units metal
atom_style atomic
create geometry
lattice fcc 5.8662
region box block -0.3 46.92 -1 68 -0.3 46.92 units box
create_box 2 box
mass 1 39.94
mass 2 195.1
potentials
pair_style hybrid eam lj/cut 10.215
pair_coeff 1 1 lj/cut 0.0104 3.405
pair_coeff 1 2 lj/cut 0.0208 2.940
pair_coeff 2 2 eam Pt_u3.eam
define groups
region 81 block INF INF 8 59 INF INF units box
create_atoms 1 region 81 units box
lattice fcc 3.9239
region 1 block INF INF 0 7.8 INF INF units box
create_atoms 2 region 1 units box
group lower region 1
region 2 block INF INF 59.2 67 INF INF units box
create_atoms 2 region 2 units box
group upper region 2
group boundary union lower upper
group flow subtract all boundary
initial velocities
compute temp_lower lower temp/com
compute temp_upper upper temp/com
compute temp_flow flow temp/com
velocity flow create 100.0 482748 units box temp temp_flow
velocity lower create 100.0 281375 units box temp temp_lower
velocity upper create 100.0 281375 units box temp temp_upper
fix 1 all nve
fix 2 flow temp/rescale 10 100.0 100.0 0.02 1.0
fix 3 lower temp/rescale 10 100.0 100.0 0.02 1.0
fix 4 upper temp/rescale 10 100.0 100.0 0.02 1.0
Run
thermo 1000
thermo_style custom step atoms temp pe ke etotal
dump 1 all xyz 1000 kapitza.xyz
timestep 0.001
Couette flow
velocity upper set 2.0 0.0 0.0 units box # add the velocity of 2.0 to upper group
fix 7 upper ave/spatial 1 1000 1000 y 59.2 7.8 vx vy vz units box norm sample file vel_upper.profile
fix 21 lower momentum 10 linear 1 1 1
fix 22 upper momentum 10 linear 0 1 1
fix 23 flow momentum 10 linear 0 1 1
run 6000000