[lammps-users] How to calculate viscosity

Hi All

I want to use “fix viscosity” command to calculate polymer’s shear viscosity.

It is mentioned in documentation that "The total momentum transferred by these velocity swaps is computed by the fix and can be output. Dividing this quantity by time and the cross-sectional area of the simulation box yields a momentum flux. The ratio of momentum flux to the slope of the shear velocity profile is the viscosity of the fluid, in appopriate units."

But I still can’t figure out how to do it.

Which argument is calculated in this command? How to get the momentum flux?

How to out put the result of a “fix” command?

Is there any easy way to get the shear rate mentioned above?