[lammps-users] Syntax error with NPT fix


I'm having a syntax issue with the NPT fix.

The command below works just fine.
fix 1 all npt temp 300.0 300.0 100.0 iso 0.0 0.0 1000.0

When I replace it with the following line I get an error, "Illegal fix nvt/npt/nph command".
fix 1 all npt temp 300.0 300.0 100.0 aniso x 0.0 0.0 1000.0 y 0.0 0.0 1000.0 z 0.0 0.0 1000.0 couple none

This appears to me to be ok from the documentation, but I don't understand this line isn't accepted. Why am I getting this error?


Nicholas Jabari Lee


The problem is aniso is incompatible with using the x, y, z notation. From the manual:

"The keyword aniso means x, y, and z dimensions are controlled independently using the Pxx, Pyy, and Pzz components of the stress tensor as the driving forces, and the specified scalar external pressure. Using “aniso Pstart Pstop Pdamp” is the same as specifying these 4 keywords:

x Pstart Pstop Pdamp
y Pstart Pstop Pdamp
z Pstart Pstop Pdamp 

couple none "