[lammps-users] npt ea


Dear Friends

I want to simulate TIP3P model of water molecule in NPT ensemble. I want to calculate some properties of water at consatant temperature and pressure but I don’t know why the pressure of the system does not reach to my desired pressure. I run 60000 fs with the following fix
fix 3 npt 293 293 100 xyz 1 1 1000
would you please help me?

Thanks alot for your time and attention.


This could be for many reasons, including the possibility
you are using red heart-shaped simulation boxes, rather than
orthogonal boxes, as in your image glyph below.

More likely, you have not equilibrated long enough or are
not adding pressure corrections if you are cutting off the
potentials, or have not used the right TIP3P params for
long-range Coulombics, etc.

Ahmed Ismail (CCd) has worked with TIP potentials
in LAMMPS and reproduced literature state points.



60 ps isn't going to get you anywhere with nose hoover. Try equilibrating at the correct density with langevin for a hundred ps or so, then use NPT.

Quoting Steve Plimpton <[email protected]>:


In addition to the comments by Matt and Steve above, I would caution you to make sure that your force field parameters are correct. There are multiple versions of the potential that go by the name TIP3P—so you also need to make sure that your choice of LJ potential is consistent with the version you’re using. (For instance, TIP3P as included in CHARMM should use pair_style lj/charmm/coul/long, while the original TIP3P of Jorgensen et all should use lj/cut/coul//ong.)