TIP4P water model

LAMMPS LAMMPS Mailing List Mirror
1

Dear LAMMPS users,

I have a question concerned with the TIP4P water model. I wonder why
the total energy in NVE simulation with TIP4P water model is not
conserved. When I did NVE simulation with TIP4P water model (12A for
L-J cutoff and 8.5A for Coulombic cutoff), the total energy was not
conserved. In stead, the kinetic energy (temperature) kept increasing.

I have used " kspace_style pppm/tip4p 10e-4", if I want to use ewald
summation in this model, can I use? how to? I think there is no option
for kspace_style.

Attached are the input script, data file and temperature file for the
TIP4P water model. Thanks.

Regards,
Farrokh

in.txt (1.32 KB)

solvate.data (143 KB)

temp.txt (3.36 KB)

2

Hi,

the pppm with the default ik differentiation cannot conserve energy.
To have a better energy conservation, you could try to use the

kspace_modify ad

command. If you want to use Ewald summation, you will have to implement
an ewald/tip4p style, similar to the pppm/tip4p.

Best,

Rolf

3

Dear LAMMPS users,

I have a question concerned with the TIP4P water model. I wonder why
the total energy in NVE simulation with TIP4P water model is not
conserved. When I did NVE simulation with TIP4P water model (12A for
L-J cutoff and 8.5A for Coulombic cutoff), the total energy was not

with a long-range solver, there is no benefit to reduce the coulomb
cutoff below the LJ cutoff. most of the computational effort lies in
looking up the coordinate data, so if you have this done for LJ
already, adding the real space for coulomb comes at little extra cost
(hence the combined pair style instead of using hybrid/overlay).

conserved. In stead, the kinetic energy (temperature) kept increasing.

I have used " kspace_style pppm/tip4p 10e-4", if I want to use ewald

your energy conservation should be much improved with using pppm/tip4p 1.e-5

no need to use that small a time step, either. when using shake. 1fs
would be a very conservative choice already.

summation in this model, can I use? how to? I think there is no option
for kspace_style.

Attached are the input script, data file and temperature file for the
TIP4P water model. Thanks.

energy conservation doesn't look too bad actually, if you discard the
first chunk. your system apparently wan't fully equilibrated.

axel.

4

Thanks Dear Rolf and Axel.

Farrokh