[lammps-users] NPT simulation


In my 2D NPT simulation, I would like to increase the pressure from 0.1 to 0.5 by:

fix 1 all npt 1.0 1.0 0.3 xy 0.1 0.5 0.1 0.5 NULL NULL 1.2
fix 2 enforce2d

When I check the thermo output, I find the pressure increases from 0.1 to about 0.35. Could anyone
tell me why it won't go to 0.5. After that, I continue the simulation from the last configuration
to increase the pressure from 0.35 to 10.5, the pressure increaes to about 7.5, not 10.5.

Thank you in advance!


Since you're getting 2/3 of the right answer each time, it looks like
fix npt aniso or xy is not averaging the 3 pressure tensor components
correctly for a 2d problem. I'll take a look.

Meanwhile, if you just run with fix npt xyz 0.1 0.5
it looks fine.


Just posted a patch (7Jul07) to make the 2d pressure calcs truly 2d,
so they don't use any z-dimension info.