unit converting between real and metal for SPC/Fw water

Please keep the loop in the list.

Is the volume changing b/c you are using fix npt?
It looks like it is changing very slowly for metal units.

If so, did you set the time constant differently
in fix npt for real vs metal units? The units
of time are fmsec vs psec for the 2 unit systems.

To get exact agreement, every LAMMPS input command
(or data file argument) that has a parameter with units,
must be converted correctly between the 2 unit choices.