new fix controller command

Hi all - FYI, we added a new fix controller command

which can be used to guide a LAMMPS simulation

to a desired target. It’s general in the sense

that you just need a quantity you can monitor,

a target value for that quantity, and some other

setting you can adjust that should push the

monitored value towards the target. The new

command does this with variables defined in your


A good example is keeping a two-phase simulation

(liquid/solid interface) stable so you can hone

in on a melting temperature. You monitor the

potential energy of the system, choose a target

where the system is half liquid/half solid, and

use a thermostat target Temp as the controller.

Another example is adjusting the position of a wall

(piston) to hold a non-periodic system at a desired


We’re hopeful other creative people (like you!)

might devise other uses for the new fix. Any

command that uses a variable as input is a candidate


Thanks to Aidan for adding this capability.