Fix SS does not allow use of dynamic group


Would you mind writing any comments how can I overcome this error?

My final goal is to find a viscosity for a region. Is it possible to compute viscosity for a region in Lammps? or does it need to do more calculation for pressure tensor in other software to get the viscosity?

a) there is no “fix SS” command in the LAMMPS distribution. Whether that command can be made compatible with dynamic groups would be a question for the developers of that command.

b) viscosity is really more a bulk property and the typical ways to compute it assume that you want to use the entire system to compute it. Limiting it to a region or group opens all kinds of difficult to answer questions about the derivation of the methods you are using that it is not recommended.

for example, attached file leads to the mentioned error! is it originated from badly using this command or other reasons? (2.7 MB) (3.9 KB)


This is a genuine error. You must not use fix ave/correlate with a dynamic group. That makes no sense at all. How can you correlate data when the dataset keeps changing?