Hi Dear Lammps users,

I want to increase the simulation box volume using change_box command, and create atoms in the new volume. I am using the following commands, but as the log file shows the zlo parameter does not change:

Commands

change_box all z delta -12.135 0 units box

change_box all boundary p p s

variable PLo equal zlo

variable PHi equal zlo+12.135

region piston block INF INF INF INF {PLo} {PHi} units box

Log File outputs

change_box all z delta -12.135 0 units box

orthogonal box = (8.35295 8.35295 0.394423) to (64.6471 64.6471 96.9706)

change_box all boundary p p s

variable PLo equal zlo

variable PHi equal zlo+12.135

region piston block INF INF INF INF {PLo} {PHi} units box

region piston block INF INF INF INF 12.533548229595021795 ${PHi} units box

region piston block INF INF INF INF 12.533548229595021795 24.668548229595021581 units box

On the other hand, if I accept that the fact that the value of zlo does not change with changing the box volume, and I use the following commands, no atoms will be created in the new volume:

Commands

change_box all z delta -12.135 0 units box

change_box all boundary p p s

variable PLo equal zlo-12.135

variable PHi equal zlo

region piston block INF INF INF INF {PLo} {PHi} units box

create_atoms 1 region piston

group piston region piston

log file

change_box all z delta -12.135 0 units box

orthogonal box = (8.35295 8.35295 0.394423) to (64.6471 64.6471 96.9706)

change_box all boundary p p s

variable PLo equal zlo-12.135

variable PHi equal zlo

region piston block INF INF INF INF {PLo} {PHi} units box

region piston block INF INF INF INF 0.39854822959502200774 ${PHi} units box

region piston block INF INF INF INF 0.39854822959502200774 12.533548229595021795 units box

create_atoms 1 region piston

Created 0 atoms

group piston region piston

0 atoms in group piston

Am I doing something wrong.

Sincerely you

Mahdi Tavakol