Dear LAMMPS Users,
I am simulating liquid flow through a nanaochanel which is confined by two walls in y and z direction respectively. The flow is along with x direction and I divided the fluid atoms into two groups including fluid group 1 and fluid group 2, in x direction. And four walls are treated as six groups with different constant temperature(T1=300K<T2<T3<T4<T5<T6).
Simulation has two stages. Firstly, no body force is added to each fluid atom in fluid group 1 or 2.Temperatures of six wall groups and fluid group 1 are controlled by using ‘fix temp/rescale’command respectively. And I only consider velocity in y and z direction when performing thermostat for fluid group 1. These thermostat control command are
compute temp_2_flow_1 group_flow_1 temp/partial 0 1 1
fix 2f_flow_1_nve group_flow_1 nve
fix 2f_flow_1 group_flow_1 temp/rescale 1 {T_fluid} {T_fluid} 0.1 1
fix_modify 2f_flow_1 temp temp_2_flow_1
In second stage, after running the input file for 80,0000 timesteps (timestep=1 fs). A body force 200X10-12N along with x direction is added to all fluid atoms in fluid group 1 and 2. In this stage, velocity in y and z direction for each fluid atom is only considered when calculating temperature. At the same time, thermostat is still conducted for fluid group 1 (300K) by using ‘fix temp/rescale’.
However, in stage 2, temperature for fluid group 1 is much higher than 300K around 5000K. I will appreciate if you can give me some suggestion. Thank you.
My input file is shown as follows.
units nano
variable T_fluid equal 300
variable T_wall_1 equal 300
variable T_wall_2 equal 330
variable T_wall_3 equal 360
variable T_wall_4 equal 390
variable T_wall_5 equal 420
variable T_wall_6 equal 450
variable spring_constant equal 500.0e3
#--------------------dimension and boundary--------------------------------------
dimension 3
boundary p p p
#--------------------definition of geometry--------------------------------------
lattice fcc 0.4
region box block 0 30 -25 25 -25 25
create_box 7 box
region hybrid block 0 30 -15 15 -15 15
region zone_flow cylinder x 0.0 0.0 3.0 0.0 12.0 units box
region zone_flow_1 cylinder x 0.0 0.0 3.0 0.0 2.0 units box
region zone_flow_2 cylinder x 0.0 0.0 3.0 2.0 12.0 units box
region zone_temp intersect 2 zone_flow box side out
region wall intersect 2 zone_temp hybrid side in
#---------------------definition of 6 walls--------------------------------------
region wall_temp_11 block 0 5 -15 15 -15 15
region wall_temp_22 block 6 10 -15 15 -15 15
region wall_temp_33 block 11 15 -15 15 -15 15
region wall_temp_44 block 16 20 -15 15 -15 15
region wall_temp_55 block 21 25 -15 15 -15 15
region wall_temp_66 block 26 30 -15 15 -15 15
region wall_1 intersect 2 wall wall_temp_11 side in
region wall_2 intersect 2 wall wall_temp_22 side in
region wall_3 intersect 2 wall wall_temp_33 side in
region wall_4 intersect 2 wall wall_temp_44 side in
region wall_5 intersect 2 wall wall_temp_55 side in
region wall_6 intersect 2 wall wall_temp_66 side in
#----------------------create atoms for each zone--------------------------------
create_atoms 1 region wall_1
create_atoms 2 region wall_2
create_atoms 3 region wall_3
create_atoms 4 region wall_4
create_atoms 5 region wall_5
create_atoms 6 region wall_6
create_atoms 7 random 7000 999999 zone_flow_1
create_atoms 7 random 10000 999999 zone_flow_2
mass 1 323.98306/1.0e6
mass 2 323.98306/1.0e6
mass 3 323.98306/1.0e6
mass 4 323.98306/1.0e6
mass 5 323.98306/1.0e6
mass 6 323.98306/1.0e6
mass 7 66.390788/1.0e6
#----------------------------groups----------------------------------------------
group group_wall_1 region wall_1
group group_wall_2 region wall_2
group group_wall_3 region wall_3
group group_wall_4 region wall_4
group group_wall_5 region wall_5
group group_wall_6 region wall_6
group group_flow region zone_flow
group group_flow_1 region zone_flow_1
group group_flow_2 region zone_flow_2
#------------------------------delete overlop atoms-----------------------------
#delete_atoms overlap 0.001 group_wall_1 group_wall_2
#delete_atoms overlap 0.001 group_wall_2 group_wall_3
#delete_atoms overlap 0.001 group_wall_3 group_wall_4
#delete_atoms overlap 0.001 group_wall_4 group_wall_5
#delete_atoms overlap o.001 group_wall_5 group_wall_6
#---------------------------potential energy model------------------------------
pair_style lj/cut 0.85125
pair_coeff * * 83.5 0.2475 0.85125
pair_coeff 7 7 1.657 0.3405 0.85125
pair_coeff *6 7 11.763 0.2940 0.85125
#--------------------------initialization velocity for each group-----------------
velocity group_wall_1 create ${T_wall_1} 999999 dist gaussian
velocity group_wall_2 create ${T_wall_2} 999999 dist gaussian
velocity group_wall_3 create ${T_wall_3} 999999 dist gaussian
velocity group_wall_4 create ${T_wall_4} 999999 dist gaussian
velocity group_wall_5 create ${T_wall_5} 999999 dist gaussian
velocity group_wall_6 create ${T_wall_6} 999999 dist gaussian
velocity group_flow_1 create ${T_fluid} 999999 dist gaussian
velocity group_flow_2 create ${T_fluid} 999999 dist gaussian
#-------------------------spring model for wall atoms-----------------------------
fix swall_1 group_wall_1 spring/self ${spring_constant}
fix swall_2 group_wall_2 spring/self ${spring_constant}
fix swall_3 group_wall_3 spring/self ${spring_constant}
fix swall_4 group_wall_4 spring/self ${spring_constant}
fix swall_5 group_wall_5 spring/self ${spring_constant}
fix swall_6 group_wall_6 spring/self ${spring_constant}
#-------------------------energy minimization-------------------------------------
minimize 1.0e-4 1.0e-6 10000 20000
min_style cg
#----------------------------temperature control----------------------------------
compute temp_wall_1 group_wall_1 temp
compute temp_wall_2 group_wall_2 temp
compute temp_wall_3 group_wall_3 temp
compute temp_wall_4 group_wall_4 temp
compute temp_wall_5 group_wall_5 temp
compute temp_wall_6 group_wall_6 temp
compute temp_flow_1 group_flow_1 temp/partial 0 1 1
fix f_wall_1 group_wall_1 nve
fix f_wall_11 group_wall_1 temp/rescale 1 {T_wall_1} {T_wall_1} 0.1 1
fix f_wall_2 group_wall_2 nve
fix f_wall_22 group_wall_2 temp/rescale 1 {T_wall_2} {T_wall_2} 0.1 1
fix f_wall_3 group_wall_3 nve
fix f_wall_33 group_wall_3 temp/rescale 1 {T_wall_3} {T_wall_3} 0.1 1
fix f_wall_4 group_wall_4 nve
fix f_wall_44 group_wall_4 temp/rescale 1 {T_wall_4} {T_wall_4} 0.1 1
fix f_wall_5 group_wall_5 nve
fix f_wall_55 group_wall_5 temp/rescale 1 {T_wall_5} {T_wall_5} 0.1 1
fix f_wall_6 group_wall_6 nve
fix f_wall_66 group_wall_6 temp/rescale 1 {T_wall_6} {T_wall_6} 0.1 1
#temperature control for liquid
fix f_flow_1_nve group_flow_1 nve
fix f_flow_1 group_flow_1 temp/rescale 1 {T_fluid} {T_fluid} 0.1 1
fix_modify f_flow_1 temp temp_flow_1
fix f_flow_2_nve group_flow_2 nve
#-----------------------------------kenitic and potential energy for all group-----
compute e_1 all ke
compute e_2 all pe
fix e all ave/time 10 4001 50000 c_e_1 c_e_2 file e_ke_po.out
#-----------------------------------equilibrium stage------------------------------
thermo_modify temp temp_flow_1
thermo 10000
timestep 1.0e-6
run 800000
#-----------------------------------flow definition--------------------------------
#fix force_flow_1 group_flow_1 addforce 200.0 0.0 0.0
#fix force_flow_2 group_flow_2 addforce 200.0 0.0 0.0
fix force_flow group_flow addforce 200.0 0.0 0.0
unfix f_flow_1_nve
unfix f_flow_1
unfix f_flow_2_nve
compute temp_2_flow_1 group_flow_1 temp/partial 0 1 1
fix 2f_flow_1_nve group_flow_1 nve
fix 2f_flow_1 group_flow_1 temp/rescale 1 {T_fluid} {T_fluid} 0.1 1
fix_modify 2f_flow_1 temp temp_2_flow_1
fix 2f_flow_2_nve group_flow_2 nve
#-----------------------------------production stage-------------------------------
#velocity of mass center for group 'group_flow-1’and ‘group_flow_2’
compute p_id_flow_1 group_flow_1 chunk/atom bin/cylinder x 0.0 2.0 0.0 0.0 0.0 3.0 1 bound x 0.0 2.0 units box
compute p_v_flow_1 group_flow_1 vcm/chunk p_id_flow_1
fix p_vv_flow_1 group_flow_1 ave/time 2 149999 300000 c_p_v_flow_1[*] file v_m_flow1.out mode vector
compute p_id_flow_2 group_flow_2 chunk/atom bin/cylinder x 2.0 10.0 0.0 0.0 0.0 3.0 1 bound x 2.0 12.0 units box
compute p_v_flow_2 group_flow_2 vcm/chunk p_id_flow_2
fix p_vv_flow_2 group_flow_2 ave/time 2 149999 300000 c_p_v_flow_2[*] file v_m_flow2.out mode vector
#temperature calculation
#method1:axial chunk
compute p_id_flow group_flow chunk/atom bin/cylinder x 0.0 0.25 0.0 0.0 0.0 3.0 1 units box
compute p_t_flow group_flow temp/partial 0 1 1
fix p_tt_flow group_flow ave/chunk 2 499999 1000000 p_id_flow vx vy vz density/number temp bias p_t_flow file T_method1.out format %20.16g
#method2:axial and radial chunk
compute p_id_1_flow group_flow chunk/atom bin/cylinder x 0.0 0.25 0.0 0.0 0.0 3.0 15 units box
compute p_t_1_flow group_flow temp/partial 0 1 1
fix p_tt_1_flow group_flow ave/chunk 2 499999 1000000 p_id_1_flow vx vy vz density/number temp bias p_t_1_flow file T_method2.out format %20.16g
#--------------------------------------kenitic energy for group_flow_2-------------
compute p_e_1 all ke
fix p_e all ave/time 2 149999 300000 c_p_e_1 file p_ke.out
#--------------------------------------run-----------------------------------------
dump 1 all atom 5000 dump.flow
thermo 10000
thermo_modify temp p_t_flow
timestep 1.0e-8
restart 200000 poly.re.out
restart 50000 p2.re.out p3.re.out
run 12000000
Best wishes,
Sun