wall/harmonic syntax

Dear all

Can anyone tell me how to write the “fix wall/harmonic” command

This is what I followed the instruction online and tried

“fix zwalls all wall/harmonic zlo 50.0 0.0 5.0 zhi 50.0 0.0 5.0 unit box”

But I always get the “illegal fix wall command” error

In my understanding the “zwalls” is the fix ID, “all” is the group ID, wall/harmonic is the fix style, “zlo” is the face, 50 is the epsilon value, 0.0 is the sigma (which is ignored according to the instruction), 5.0 is the cutoff distance. And at last I set up the unit the same as the box unit

Is there any mistake in my input?

Thank you very much

Jing

Sorry I put my command wrong in the previous email

It is
“variable lo equal zlo
variable hi equal zhi
fix zwalls all wall/harmonic zlo v_lo 50.0 0.0 5.0 zhi v_hi 50.0 0.0 5.0 unit box"

Thank you again

The keyword is units not unit.

Steve