I was trying to simulate the Couette flow problem for different wall velocities. I had initially used a damping factor for 'fix langevin' as 1.0 to maintain a temperature of 1.1 (in lj units) it was working fine for lower velocities but at higher velocities the temperature started rising above the thermostated temperature. Hence I changed the damping factor to 200. But now it is not thermostating properly for even lower temperatures. I have pasted the log files for both the cases below.
I am trying to figure first how to choose a damping factor to get the correct thermostating. Secondly if at all the problem is because of damping factor.
I tried looking through few literature but they did not have anything on how to choose a damping factor.
I would highly appreciate it if anyone could help me or atleast guide me as to where I could find the answer for it.
Thank you.
BR/Joseph
1) DAMPING FACTOR = 1.0
LAMMPS (9 Mar 2011)
# 3-d LJ flow simulation
units lj
dimension 3
boundary p s p
atom_style atomic
neighbor 0.3 bin
neigh_modify delay 1
# create geometry
region fluid block 0 11.95 1.5 26.07 0.0 7.22 units box
region btm_wall block 0 11.95 0 1.5 0.0 7.22 units box
region top_wall block 0 11.95 26.07 28.0 0.0 7.22 units box
region simulation_box union 3 btm_wall fluid top_wall units box
create_box 3 simulation_box
Created orthogonal box = (0 0 0) to (11.95 28 7.22)
1 by 1 by 1 processor grid
lattice fcc 0.81 orient x 1 1 -2 orient y 1 1 1 orient z 1 -1 0
Lattice spacing in x,y,z = 2.78084 2.94953 2.40828
create_atoms 1 region fluid units box
Created 1735 atoms
lattice fcc 3.24 orient x -1 1 0 orient y 1 1 1 orient z 1 1 -2
Lattice spacing in x,y,z = 1.51712 1.85809 1.75182
create_atoms 2 region btm_wall units box
Created 488 atoms
lattice fcc 3.24 orient x -1 1 0 orient y 1 1 1 orient z 1 1 -2
Lattice spacing in x,y,z = 1.51712 1.85809 1.75182
create_atoms 3 region top_wall units box
Created 528 atoms
mass 1 1.0
mass 2 4.0
mass 3 4.0
# LJ potentials
pair_style lj/cut 2.2
pair_coeff * * 1.0 1.0
pair_coeff 1 2*3 0.2 0.75
pair_modify shift yes
# define groups
region 1 block INF INF INF 1.5 INF INF units box
group lower region 1
488 atoms in group lower
region 2 block INF INF 26.07 INF INF INF units box
group upper region 2
528 atoms in group upper
group boundary union lower upper
1016 atoms in group boundary
group flow subtract all boundary
1735 atoms in group flow
set group lower type 2
488 settings made for type
set group upper type 3
528 settings made for type
# initial velocities
compute mobile flow temp/partial 0 0 1
fix 2 flow langevin 1.10 1.10 1.0 699483
velocity flow create 1.1 482748 temp mobile units box
fix 1 all nve
#fix 2 flow temp/rescale 200 1.1 1.1 0.02 1.0
fix_modify 2 temp mobile
# Couette flow
velocity lower set 0.0 0.0 0.0 units box
velocity upper set 1.0 0.0 0.0 units box
fix 3 boundary setforce 0.0 0.0 0.0
#fix test boundary spring tether 1200.0 0.0 0.0 0.0 0.0
#fix test boundary spring/self 1200.0
#fix test1 upper spring tether 1.0 0.0 0.0 0.0 0.0
#fix 4 all enforce2d
group tp_wall region top_wall
528 atoms in group tp_wall
#fluid adjacent to bottom wall
fix 5 flow ave/spatial 1 300000 300000 x center 11.95 z center 7.22 y 1.5 1.02375 vx region fluid file vel_fb.profile units box
# Poiseuille flow
#velocity boundary set 0.0 0.0 0.0
#fix 3 lower setforce 0.0 0.0 0.0
#fix 4 upper setforce 0.0 NULL 0.0
#fix 5 upper aveforce 0.0 -1.0 0.0
#fix 6 flow addforce 0.5 0.0 0.0
#fix 7 all enforce2d
# Run
compute btm_wall_temp lower temp
compute tp_wall_temp upper temp
timestep 0.005
thermo 5000
#thermo_style custom step temp evdwl ecoul epair ebond edihed eimp eangle emol etotal
thermo_style custom step temp etotal c_btm_wall_temp c_tp_wall_temp
thermo_modify temp mobile
WARNING: Temperature for thermo pressure is not for group all
#dump 1 all atom 10 dump.flow
#dump 2 boundary custom 1000 dump.flow2 ys vx
run 600000
Memory usage per processor = 2.279 Mbytes
Step Temp TotEng btm_wall tp_wall_
0 1.1 257.46174 0 1.3358634
5000 1.0507066 253.59773 0 1.3358634
10000 1.119441 253.64237 0 1.3358634
15000 1.1345931 253.64325 0 1.3358634
20000 1.1695244 253.65465 0 1.3358634
25000 1.1085835 253.62149 0 1.3358634
30000 1.1197047 253.64191 0 1.3358634
35000 0.99935069 253.6087 0 1.3358634
40000 1.1656417 253.62 0 1.3358634
45000 1.0752766 253.59682 0 1.3358634
50000 1.1531744 253.64117 0 1.3358634
55000 1.1051872 253.64553 0 1.3358634
60000 1.1343677 253.64065 0 1.3358634
65000 1.0446773 253.61951 0 1.3358634
70000 1.1017815 253.62925 0 1.3358634
75000 1.0829796 253.65731 0 1.3358634
80000 1.1071206 253.60033 0 1.3358634
85000 1.1652198 253.63025 0 1.3358634
90000 1.0765965 253.62754 0 1.3358634
95000 1.1394094 253.63398 0 1.3358634
100000 1.2046504 253.66938 0 1.3358634
105000 1.1370375 253.65422 0 1.3358634
110000 1.1512951 253.64267 0 1.3358634
115000 1.1052644 253.6232 0 1.3358634
120000 1.1084717 253.63155 0 1.3358634
125000 1.0602751 253.64317 0 1.3358634
130000 1.0994552 253.63097 0 1.3358634
135000 1.0230237 253.57474 0 1.3358634
140000 1.1080874 253.65086 0 1.3358634
145000 1.0801643 253.6498 0 1.3358634
150000 1.1060963 253.62251 0 1.3358634
155000 1.1085059 253.61981 0 1.3358634
160000 1.1746287 253.65529 0 1.3358634
165000 1.1133475 253.63473 0 1.3358634
170000 1.10359 253.6429 0 1.3358634
175000 1.1018195 253.62811 0 1.3358634
180000 1.2030303 253.66308 0 1.3358634
185000 1.1708241 253.64755 0 1.3358634
190000 1.1235511 253.64398 0 1.3358634
195000 1.0375278 253.59636 0 1.3358634
200000 1.112392 253.64573 0 1.3358634
205000 1.0676118 253.63431 0 1.3358634
210000 1.1003571 253.63684 0 1.3358634
215000 1.0606753 253.60694 0 1.3358634
220000 1.0423592 253.62073 0 1.3358634
225000 1.1113113 253.63484 0 1.3358634
230000 1.0939753 253.6367 0 1.3358634
235000 1.0941297 253.63796 0 1.3358634
240000 1.0748566 253.6222 0 1.3358634
245000 1.0947193 253.6167 0 1.3358634
250000 1.0873131 253.62322 0 1.3358634
255000 1.0857788 253.6571 0 1.3358634
260000 1.066238 253.60951 0 1.3358634
265000 1.1242448 253.62895 0 1.3358634
270000 1.0942999 253.63151 0 1.3358634
275000 1.0654069 253.59644 0 1.3358634
280000 1.104333 253.6387 0 1.3358634
285000 1.0833966 253.62006 0 1.3358634
290000 1.1601746 253.64821 0 1.3358634
295000 1.0372644 253.62829 0 1.3358634
300000 1.0607024 253.59742 0 1.3358634
305000 1.1266566 253.62612 0 1.3358634
310000 1.0690641 253.58942 0 1.3358634
315000 1.0934018 253.64517 0 1.3358634
320000 1.1705221 253.62429 0 1.3358634
325000 1.0707689 253.6143 0 1.3358634
330000 1.0572419 253.62974 0 1.3358634
335000 1.0981461 253.63071 0 1.3358634
340000 1.158883 253.64555 0 1.3358634
345000 1.128077 253.67453 0 1.3358634
350000 1.048313 253.63165 0 1.3358634
355000 1.0425548 253.58352 0 1.3358634
360000 1.0751429 253.62552 0 1.3358634
365000 1.0270802 253.60124 0 1.3358634
370000 1.1183242 253.63426 0 1.3358634
375000 1.1454907 253.66511 0 1.3358634
380000 1.1056002 253.62272 0 1.3358634
385000 1.1314341 253.65042 0 1.3358634
390000 1.0968005 253.60388 0 1.3358634
395000 1.1201174 253.6221 0 1.3358634
400000 1.1177679 253.63908 0 1.3358634
405000 1.0700923 253.60885 0 1.3358634
410000 1.1649264 253.64314 0 1.3358634
415000 1.1197772 253.62997 0 1.3358634
420000 1.0591472 253.62321 0 1.3358634
425000 1.1056556 253.63176 0 1.3358634
430000 1.0961797 253.62662 0 1.3358634
435000 1.1353169 253.6603 0 1.3358634
440000 1.0606554 253.62831 0 1.3358634
445000 1.0815593 253.64086 0 1.3358634
450000 1.0980837 253.67363 0 1.3358634
455000 1.1051909 253.62842 0 1.3358634
460000 1.1496605 253.61554 0 1.3358634
465000 1.1243858 253.6196 0 1.3358634
470000 1.0780363 253.64051 0 1.3358634
475000 1.1619706 253.65592 0 1.3358634
480000 1.1593298 253.64164 0 1.3358634
485000 1.1552987 253.63647 0 1.3358634
490000 1.1124164 253.62196 0 1.3358634
495000 1.1234938 253.63363 0 1.3358634
500000 1.1021301 253.63478 0 1.3358634
505000 1.0544891 253.58152 0 1.3358634
510000 1.1071074 253.64739 0 1.3358634
515000 1.1017781 253.6333 0 1.3358634
520000 1.0973214 253.65119 0 1.3358634
525000 1.1232451 253.631 0 1.3358634
530000 1.1537653 253.66298 0 1.3358634
535000 1.0641569 253.62146 0 1.3358634
540000 1.1733724 253.65925 0 1.3358634
545000 1.1148625 253.62459 0 1.3358634
550000 1.1816796 253.66888 0 1.3358634
555000 1.1238443 253.62949 0 1.3358634
560000 1.1381152 253.66116 0 1.3358634
565000 1.1037682 253.64093 0 1.3358634
570000 1.1074723 253.61416 0 1.3358634
575000 1.0760858 253.60255 0 1.3358634
580000 1.057463 253.65259 0 1.3358634
585000 1.0474823 253.60015 0 1.3358634
590000 1.1352097 253.64222 0 1.3358634
595000 1.0711174 253.62577 0 1.3358634
600000 1.1485206 253.64896 0 1.3358634
Loop time of 3607.86 on 1 procs for 600000 steps with 2751 atoms
Pair time (\) = 2475\.75 \(68\.6208\)
Neigh time \() = 775.746 (21.5015)
Comm time (\) = 82\.3773 \(2\.28327\)
Outpt time \() = 0.00913143 (0.000253098)
Other time (%) = 273.986 (7.59413)
Nlocal: 2751 ave 2751 max 2751 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Nghost: 3903 ave 3903 max 3903 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Neighs: 108729 ave 108729 max 108729 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Total # of neighbors = 108729
Ave neighs/atom = 39.5234
Neighbor list builds = 86343
Dangerous builds = 0
2) DAMPING FACTOR = 200.0
LAMMPS (9 Mar 2011)
# 3-d LJ flow simulation
units lj
dimension 3
boundary p s p
atom_style atomic
neighbor 0.3 bin
neigh_modify delay 1
# create geometry
region fluid block 0 11.95 1.5 26.07 0.0 7.22 units box
region btm_wall block 0 11.95 0 1.5 0.0 7.22 units box
region top_wall block 0 11.95 26.07 28.0 0.0 7.22 units box
region simulation_box union 3 btm_wall fluid top_wall units box
create_box 3 simulation_box
Created orthogonal box = (0 0 0) to (11.95 28 7.22)
1 by 1 by 1 processor grid
lattice fcc 0.81 orient x 1 1 -2 orient y 1 1 1 orient z 1 -1 0
Lattice spacing in x,y,z = 2.78084 2.94953 2.40828
create_atoms 1 region fluid units box
Created 1735 atoms
lattice fcc 3.24 orient x -1 1 0 orient y 1 1 1 orient z 1 1 -2
Lattice spacing in x,y,z = 1.51712 1.85809 1.75182
create_atoms 2 region btm_wall units box
Created 488 atoms
lattice fcc 3.24 orient x -1 1 0 orient y 1 1 1 orient z 1 1 -2
Lattice spacing in x,y,z = 1.51712 1.85809 1.75182
create_atoms 3 region top_wall units box
Created 528 atoms
mass 1 1.0
mass 2 4.0
mass 3 4.0
# LJ potentials
pair_style lj/cut 2.2
pair_coeff * * 1.0 1.0
pair_coeff 1 2*3 0.2 0.75
pair_modify shift yes
# define groups
region 1 block INF INF INF 1.5 INF INF units box
group lower region 1
488 atoms in group lower
region 2 block INF INF 26.07 INF INF INF units box
group upper region 2
528 atoms in group upper
group boundary union lower upper
1016 atoms in group boundary
group flow subtract all boundary
1735 atoms in group flow
set group lower type 2
488 settings made for type
set group upper type 3
528 settings made for type
# initial velocities
compute mobile flow temp/partial 0 0 1
fix 2 flow langevin 1.10 1.10 200.0 699483
velocity flow create 1.1 482748 temp mobile units box
fix 1 all nve
#fix 2 flow temp/rescale 200 1.1 1.1 0.02 1.0
fix_modify 2 temp mobile
# Couette flow
velocity lower set 0.0 0.0 0.0 units box
velocity upper set 1.0 0.0 0.0 units box
fix 3 boundary setforce 0.0 0.0 0.0
#fix test boundary spring tether 1200.0 0.0 0.0 0.0 0.0
#fix test boundary spring/self 1200.0
#fix test1 upper spring tether 1.0 0.0 0.0 0.0 0.0
#fix 4 all enforce2d
group tp_wall region top_wall
528 atoms in group tp_wall
#fluid adjacent to bottom wall
fix 5 flow ave/spatial 1 300000 300000 x center 11.95 z center 7.22 y 1.5 1.02375 vx region fluid file vel_fb.profile units box
# Poiseuille flow
#velocity boundary set 0.0 0.0 0.0
#fix 3 lower setforce 0.0 0.0 0.0
#fix 4 upper setforce 0.0 NULL 0.0
#fix 5 upper aveforce 0.0 -1.0 0.0
#fix 6 flow addforce 0.5 0.0 0.0
#fix 7 all enforce2d
# Run
compute btm_wall_temp lower temp
compute tp_wall_temp upper temp
timestep 0.005
thermo 5000
#thermo_style custom step temp evdwl ecoul epair ebond edihed eimp eangle emol etotal
thermo_style custom step temp etotal c_btm_wall_temp c_tp_wall_temp
thermo_modify temp mobile
WARNING: Temperature for thermo pressure is not for group all
#dump 1 all atom 10 dump.flow
#dump 2 boundary custom 1000 dump.flow2 ys vx
run 600000
Memory usage per processor = 2.279 Mbytes
Step Temp TotEng btm_wall tp_wall_
0 1.1 257.46174 0 1.3358634
5000 3.6850092 255.54112 0 1.3358634
10000 3.4427466 255.47905 0 1.3358634
15000 3.2906173 255.4262 0 1.3358634
20000 3.3313931 255.36402 0 1.3358634
25000 3.0877226 255.27732 0 1.3358634
30000 3.1103855 255.22944 0 1.3358634
35000 3.1430747 255.21199 0 1.3358634
40000 2.9950076 255.16079 0 1.3358634
45000 3.076996 255.09321 0 1.3358634
50000 2.9063887 254.99931 0 1.3358634
55000 2.8325882 254.96636 0 1.3358634
60000 2.7474052 254.94376 0 1.3358634
65000 2.6343302 254.87853 0 1.3358634
70000 2.6894837 254.88623 0 1.3358634
75000 2.7328451 254.8699 0 1.3358634
80000 2.5975051 254.79235 0 1.3358634
85000 2.5416281 254.75219 0 1.3358634
90000 2.5226608 254.70134 0 1.3358634
95000 2.380419 254.671 0 1.3358634
100000 2.4340323 254.62701 0 1.3358634
105000 2.4168633 254.65589 0 1.3358634
110000 2.4166323 254.63897 0 1.3358634
115000 2.333767 254.54008 0 1.3358634
120000 2.1627583 254.54022 0 1.3358634
125000 2.2224634 254.53014 0 1.3358634
130000 2.1362109 254.47564 0 1.3358634
135000 2.2141369 254.4969 0 1.3358634
140000 2.1481779 254.49073 0 1.3358634
145000 2.1184305 254.47344 0 1.3358634
150000 2.0908449 254.40747 0 1.3358634
155000 2.1095118 254.39408 0 1.3358634
160000 2.0502686 254.38688 0 1.3358634
165000 2.0427149 254.39993 0 1.3358634
170000 2.0222356 254.4061 0 1.3358634
175000 1.851475 254.3329 0 1.3358634
180000 1.8767894 254.31187 0 1.3358634
185000 2.0041082 254.34936 0 1.3358634
190000 1.9769428 254.3108 0 1.3358634
195000 1.9720032 254.31035 0 1.3358634
200000 1.9395832 254.30883 0 1.3358634
205000 1.9055985 254.30251 0 1.3358634
210000 1.8615501 254.28273 0 1.3358634
215000 1.9342401 254.26974 0 1.3358634
220000 1.8152695 254.23856 0 1.3358634
225000 1.8161752 254.22208 0 1.3358634
230000 1.7700137 254.19309 0 1.3358634
235000 1.8820712 254.26496 0 1.3358634
240000 1.7847464 254.22815 0 1.3358634
245000 1.723447 254.17834 0 1.3358634
250000 1.8269488 254.20779 0 1.3358634
255000 1.7147963 254.17936 0 1.3358634
260000 1.7738313 254.16994 0 1.3358634
265000 1.7807508 254.17219 0 1.3358634
270000 1.7437417 254.16394 0 1.3358634
275000 1.7820841 254.18265 0 1.3358634
280000 1.890526 254.23986 0 1.3358634
285000 1.7904153 254.19801 0 1.3358634
290000 1.7849692 254.19833 0 1.3358634
295000 1.7200384 254.14411 0 1.3358634
300000 1.8260603 254.18023 0 1.3358634
305000 1.7736183 254.17304 0 1.3358634
310000 1.792293 254.16729 0 1.3358634
315000 1.7932311 254.18541 0 1.3358634
320000 1.7417411 254.18391 0 1.3358634
325000 1.7630283 254.18875 0 1.3358634
330000 1.6243078 254.14503 0 1.3358634
335000 1.6975884 254.14633 0 1.3358634
340000 1.6657034 254.14339 0 1.3358634
345000 1.7508922 254.16674 0 1.3358634
350000 1.6659771 254.12424 0 1.3358634
355000 1.7454423 254.16448 0 1.3358634
360000 1.7479471 254.15363 0 1.3358634
365000 1.6637722 254.13866 0 1.3358634
370000 1.7037321 254.16761 0 1.3358634
375000 1.7419778 254.13613 0 1.3358634
380000 1.7018366 254.11524 0 1.3358634
385000 1.6108149 254.10571 0 1.3358634
390000 1.6760946 254.14707 0 1.3358634
395000 1.6482118 254.10411 0 1.3358634
400000 1.7010636 254.13287 0 1.3358634
405000 1.7225569 254.16716 0 1.3358634
410000 1.7121818 254.11904 0 1.3358634
415000 1.6305814 254.10117 0 1.3358634
420000 1.7124906 254.12982 0 1.3358634
425000 1.7013314 254.11615 0 1.3358634
430000 1.6985962 254.13318 0 1.3358634
435000 1.6765235 254.13651 0 1.3358634
440000 1.6870726 254.13141 0 1.3358634
445000 1.7100994 254.15822 0 1.3358634
450000 1.6950602 254.14231 0 1.3358634
455000 1.6458774 254.14076 0 1.3358634
460000 1.6672891 254.11507 0 1.3358634
465000 1.7029693 254.12265 0 1.3358634
470000 1.6769669 254.12759 0 1.3358634
475000 1.6902899 254.14778 0 1.3358634
480000 1.8087404 254.16291 0 1.3358634
485000 1.7057856 254.14436 0 1.3358634
490000 1.7047077 254.16115 0 1.3358634
495000 1.696784 254.1587 0 1.3358634
500000 1.6681386 254.10746 0 1.3358634
505000 1.7248573 254.15119 0 1.3358634
510000 1.8309149 254.16192 0 1.3358634
515000 1.7667819 254.16063 0 1.3358634
520000 1.809362 254.14385 0 1.3358634
525000 1.8066829 254.14909 0 1.3358634
530000 1.7802298 254.17875 0 1.3358634
535000 1.7056583 254.12645 0 1.3358634
540000 1.6639387 254.13834 0 1.3358634
545000 1.6975207 254.13806 0 1.3358634
550000 1.7102981 254.12988 0 1.3358634
555000 1.6083625 254.10242 0 1.3358634
560000 1.6943896 254.12556 0 1.3358634
565000 1.6629248 254.08204 0 1.3358634
570000 1.7004332 254.08827 0 1.3358634
575000 1.8162499 254.1349 0 1.3358634
580000 1.6975856 254.14093 0 1.3358634
585000 1.7500516 254.14761 0 1.3358634
590000 1.7651969 254.14513 0 1.3358634
595000 1.7367473 254.13139 0 1.3358634
600000 1.6667598 254.10152 0 1.3358634
Loop time of 3907.21 on 1 procs for 600000 steps with 2751 atoms
Pair time (\) = 2532\.75 \(64\.8224\)
Neigh time \() = 1008.83 (25.8198)
Comm time (\) = 88\.4435 \(2\.2636\)
Outpt time \() = 0.00927567 (0.000237399)
Other time (%) = 277.176 (7.09395)
Nlocal: 2751 ave 2751 max 2751 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Nghost: 3906 ave 3906 max 3906 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Neighs: 108457 ave 108457 max 108457 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Total # of neighbors = 108457
Ave neighs/atom = 39.4246
Neighbor list builds = 111073
Dangerous builds = 0