[lammps-users] Fix npt command for a system with solvent

Hi,

I am using LAMMPS to simulate a system with solvent (water), and I do not know which fix command I should use
fix 1 water npt …
fix 1 water npt/asphere …
fix 1 water npt/sphere …

Thanks

2009/12/3 Jervis Chu <[email protected]…1193…>

Hi,

I am using LAMMPS to simulate a system with solvent (water), and I do not know which fix command I should use
fix 1 water npt …
fix 1 water npt/asphere …
fix 1 water npt/sphere …

Jervis:

From the manual for fix npt:

“Perform constant NPT integration to update positions and velocities each timestep for atoms in the group using a Nose/Hoover temperature thermostat (Hoover1) and Nose/Hoover pressure barostat (Hoover2), implemented as described in (Melchionna). P is pressure; T is temperature. This creates a system trajectory consistent with the isothermal-isobaric ensemble.”

for fix npt/asphere:

“Perform constant NPT integration to update position, velocity, orientation, and angular velocity each timestep for aspherical or ellipsoidal particles in the group using a Nose/Hoover temperature thermostat and Nose/Hoover pressure barostat. P is pressure; T is temperature. This creates a system trajectory consistent with the isothermal-isobaric ensemble.”

and fix npt/sphere:

"Perform constant NPT integration to update position, velocity, and angular velocity each timestep for extended spherical particles in the group using a Nose/Hoover temperature thermostat and Nose/Hoover pressure barostat. P is pressure; T is temperature. This creates a system trajectory consistent with the isothermal-isobaric ensemble.

This fix differs from the fix npt command, which assumes point particles and only updates their position and velocity."

So, based on your model for water, which model works best? Does your model assume the atoms are point particles, spheres, or ellipsoids?

–AEI