SPC Water Model Minimization

LAMMPS LAMMPS Beginners
1

Hello,

I just tried to do a SPC Water Model by following the LAMMPS manual (8.4.6. SPC water model — LAMMPS documentation), I only changed the number of water molecules to 1000, I increased the size of the box to have the right density, and I computed the radial distribution function. However, I get a jump to 1.5 at the cutoff distance for my rdf, instead of a stabilization at 1. I think it is because I get this message during the minimization: Minimization stats:
Stopping criterion = linesearch alpha is zero
So, my Totenergy is still at 3700 when the minimization stops… Did my simulation stopped at a local minimization instead of a global one ? If so, how to have the global minimization?

2

You are not providing the exact input and showing how to exactly reproduce what you are seeing.
The initial coordinates in these example inputs will be random and thus computing a g(r) from those is a pointless exercise. You first need to run an equilibration and after that collect the g(r) data over some time to get well converged data from averaging.

Please also note that the most effective way of creating a larger initial system is to first equilibrate a smaller system and then use the replicate command and equlibrate a little more after that.

3

Thank you !