viscosity via fix deform+implicit solvent / temperature issues

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1

Dear Lammps-Users,

I have been working towards calculation of viscosity of spherical colloidal particles using lammps via fix deform/box deformation method. I am having trouble controlling the temperature of my simulation system.

When I start the simulation and equilibrate the system via fix nve/langevin combination, the system fluctuates near desired temperature…

Step Temp PotEng KinEng TotEng Volume Press Density Lx Ly Lz
0 293.15 -0.12767348 10485.02 10484.892 3000000 159.759 1.4739087 200 150 100

100000 295.66051 13.806628 10574.812 10588.619 3000000 162.61987 1.4739087 200 150 100

…but when I start the dynamics and continue with fix nvt/sllod, fix deform and thermo_modify temp tilt …

fix 1 all nvt/sllod temp $T T 10.0** **fix 2 all deform 1 xy erate {xyrate} remap v
compute tilt all temp/deform
…The temperature go haywire and produce very weird temperature scales…as you can see below…
Step Temp c_usual PotEng TotEng Press Volume Density Pxy
0 4.2949786e+09 293.15 13.806628 1.5361738e+11 2.3407334e+09 3000000 1.4739087 -14333.337
1000 0.015867274 4.2949592e+09 4663.6396 4664.2071 428.3836 3000000 1.4739087 -296.23367
2000 0.019312198 4.2961639e+09 4003.8359 4004.5266 367.81751 3000000 1.4739087 -264.03971
3000 0.033997626 4.296414e+09 7143.45 7144.6659 655.79255 3000000 1.4739087 -442.22302
4000 0.024984739 4.2964145e+09 4205.5584 4206.452 386.34433 3000000 1.4739087 -317.34612
5000 0.0079016446 4.2959051e+09 3260.3266 3260.6092 299.873 3000000 1.4739087 -144.8736
6000 0.0095063252 4.2959047e+09 3222.4306 3222.7706 296.37825 3000000 1.4739087 -165.70544
7000 0.015150939 4.2959054e+09 4979.2388 4979.7807 457.39181 3000000 1.4739087 -263.68253
8000 0.0062240888 4.2956523e+09 3564.6123 3564.8349 327.92871 3000000 1.4739087 -99.314651
9000 0.0025053293 4.2956511e+09 2076.462 2076.5516 191.36842 3000000 1.4739087 -41.894239
10000 0.0031442948 4.295902e+09 2069.961 2070.0735 190.68147 3000000 1.4739087 -57.838724

…and continue the same in the data collection run.

Attached is the input script I am using for the run. Could anyone please give me a hint what am I doing wrong here??

on another note, It may be very lame question(apologies in advance) but even after using nvt/sllod , Am I still doing implicit solvent simulation?? (I want to run implicit solvent only).

Every bit of help and suggestion is greatly appreciated.

Thanking you

Best
Raghvendra

temp_defom.in (5.09 KB)

2

Yes, fix nvt/sllod can be a model for implicit solvent. If you did not
change your system at all (move atoms, reassign velocities, change
the pair style) before the start of your 2nd run, you should get
the same temp and pot eng on step 0 of the 2nd run
as on the last step of the 1st run. Clearly that is not happening.
So you should try to figure out what changes or new command(s)
are causing this. Try commenting them out one at a time
to see what gives.a consistent step 0 (2nd run) with last step (1st run).

Steve