Getting out of range atom for using fix wall/region and region sphere

LAMMPS LAMMPS Beginners
1

Dear All,

I have used a simple examination on using fix wall/region. Hereby, I put a water droplet on substrate and tried to fix it with harmonic potential. So, I followed the lammps documentation and defined a region and too large epsilon (Attached Files)

region le_sphere sphere 49.0 50.0 28.0 29.0 side in
fix wall1 water wall/region le_sphere harmonic 1000000.0 0.0 2.5

Unfortunately I got the error: “Out of range atoms - cannot compute PPPM”. So, I reduced the cutoff radius to 1 A. In this case, it goes for 7000 steps and again stops with the similar error.

In addition, I checked the structure and run the program without fix wall/region command. There were no problem. In this way, I think there is something wrong with defining region sphere and using fix wall/region. Any comments will be appreciated…

Best wishes

wetting.data (1.1 MB)
wet.in (1.7 KB)

2

In my opinion, the reason of getting this error is because of the nature of harmonic potential (especially stops running after 7000 steps). And, this may not originate from the structure and the option of fix wall/region.

So, to fix the water droplet on the substrate during the NVT equilibration, I used fix spring command. It seems it works. However, I do not exactly know for defining surface soft harmonic potential which one is standard? fix spring or fix wall/region?

Thanks for your valuable comments