about increasing Nevery

Dear all,

I tried to calculate the shear viscosity using rNEMD method. Using following command:

fix 2 all ave/spatial 100 1000 100000 z lower 0.05 vx file visc.profile units box
fix 3 all viscosity 100 x z 20 swap 1 vtarget 1.5

I got the velocity slope dvx/dz slightly non-linear. Based on the lammps manual, I should increase Nevery number. So I increased it to 200. Then when I tested it, I got the error message of Illegal fix ave/spatial command. Even after increasing the number of others, it still showed me the same error. I used lammps-8Jun11 edition. Can I get some help here? Thanks a lot.

Laura

If you're saying that your input script ran fine,
you changed Nevery in the fix viscosity command,
then you get an error with the fix ave/spatial command,
that doesn't make sense. The two fixes are unrelated.

I don't think you are providing enough info to answer
your question.

Steve

Hi, Steve:

Thanks a lot for trying to answer my question. In order to make the dvx/dz slope linear, I increased the Nevery in the fix ave/spatial command to following:
fix 2 all ave/spatial 200 1000 100000 z lower 0.05 vx file visc.profile units box
fix 3 all viscosity 100 x z 20 swap 1 vtarget 1.5

and also tried following:

fix 2 all ave/spatial 200 2000 200000 z lower 0.05 vx file visc.profile units box
fix 3 all viscosity 100 x z 20 swap 1 vtarget 1.5

with all others unchanged. I got the error as Illegal fix ave/spatial command. The simulation can not run at all. I really can not understand why.

best,

Laura

The product of the first 2 numbers in the fix ave/spatial command
needs to be smaller than the 3rd number, The
doc page explains why.

Steve