Dear LAMMPS users,
I have difficulty interpreting the behavior of my system, and would be very grateful if you help me in this regard.
The system is composed of a solid surface (NiS (100)) in contact with approximately 6000 water molecules. In some cases organic ions are also included within the liquid region. Due to periodic boundary conditions, vacuum of 100A thickness is applied along the z direction to avoid the interactions of the liquid particles with the other side of the solid surface. However, as the dynamic run through the NPT ensemble progresses (at 0 pressure), the box shrinks in z direction, until the vacuum space disappears and the liquid gets in contact with the bottom of the solid surface. Could you please help me understand the reason? Does this behavior refer to the high energy of the surface?
Best regards,
Monir
Dear LAMMPS users,
I have difficulty interpreting the behavior of my system, and would be very grateful if you help me in this regard.
The system is composed of a solid surface (NiS (100)) in contact with approximately 6000 water molecules. In some cases organic ions are also included within the liquid region. Due to periodic boundary conditions, vacuum of 100A thickness is applied along the z direction to avoid the interactions of the liquid particles with the other side of the solid surface. However, as the dynamic run through the NPT ensemble progresses (at 0 pressure), the box shrinks in z direction, until the vacuum space disappears and the liquid gets in contact with the bottom of the solid surface. Could you please help me understand the reason? Does this behavior refer to the high energy of the surface?
no, this is just due to incorrect use of fix npt: you must not couple the z-direction to the barostat. for a solid it also makes little sense to use a variable cell in the first place. finally, are you aware of the “kspace_modify slab” option which uses a poisson solver to cancel the periodic interaction of the dipole forming in the slab configuration? for the water/vacuum interface, it is advisable to place a suitable soft reflective wall into the system to avoid that evaporated water molecules go into the vacuum zone added for the poisson solver (which must remain empty for it to work correctly).
axel.