A question about OPLSAA+TIP4P

Dear all:

I try to use OPLSAA forcefield combine with TIP4P water model. But after minimization, the O atoms between two molecules are suck together and an error raise"out of range, cannot compute PPPM".

OPLSAA does have TIP4P and SPC parameters, and it just uses pair_style lj/cut/coul/long. I using moltemplate’s oplsaa.lt to generate the whole simulation system, but SPC is fine and TIP4P has the error. So I don’t think its forcefield is fine.

The biggest problem may be whether to explicitly add dummy atom when modeling (H-(OM)-H). The how-to page says that under pair_style lj/cut/tip4p/long, the LAMMPS can add it automatically, but OPLSAA is using lj/cut/coul/long.

This question has been bothering me for several days, and I hope anyone with experience can help me solve this problem

Thanks in advance. If any information needed I would send it to you as soon as possible!

Roy Kid

Dear all:

I try to use OPLSAA forcefield combine with TIP4P water model. But after minimization, the O atoms between two molecules are suck together and an error raise"out of range, cannot compute PPPM".

that seems to indicate some problem with your force field parameter assignment. but that is difficult to assess from remote with just this rather vague description and without knowing more details.

OPLSAA does have TIP4P and SPC parameters, and it just uses pair_style lj/cut/coul/long. I using moltemplate’s oplsaa.lt to generate the whole simulation system, but SPC is fine and TIP4P has the error. So I don’t think its forcefield is fine.

The biggest problem may be whether to explicitly add dummy atom when modeling (H-(OM)-H). The how-to page says that under pair_style lj/cut/tip4p/long, the LAMMPS can add it automatically, but OPLSAA is using lj/cut/coul/long.

you are not paying enough attention to the explanations in the documentation. pair style lj/cut/tip4p/long is the same as lj/cut/coul/long for all atoms except those flagged as the water hydrogen and oxygen, where the charge interaction is altered to compute it on the M position instead of the O position.

This question has been bothering me for several days, and I hope anyone with experience can help me solve this problem

you may be looking in the wrong place.

axel.