ReaxFF for charged system

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1

Dear all

I have a system consisting of water molecules and a single OH- ion. Since the system is not neutral can I do a ReaxFF with qeq? Similar questions asked previously (http://lammps.sandia.gov/threads/msg50996.html, http://lammps.sandia.gov/threads/msg20851.html) have been advised not to run ReaxFF for charged system. What modifications must me made to use qeq/reax for my system. Is it possible to run ReaxFF for such a sytem in LAMMPS?

Thanks
Vaishali

2

fix qeq/dynamic might solve this issue ?

3

fix qeq/dynamic might solve this issue ?

you *must* use fix qeq/reax with pair reax/c. it is enforced by the code.

axel.

4

Hi

Since qeq/reax must be used with pair/reax …does this mean it is not possible to run ReaxFF for a charged system (a single hydroxide ion in a water system) in LAMMPS. If yes, how to implement it ?

Thanks
Vaishali

5

No, it is not possible to run ReaxFF for a charged system since fix qeq/reax neutralizes the system at the beginning. Due to numerical instabilities with the matrix inversion method used by fix qeq/reax, charge neutrality is strictly enforced. There is no way around it.

Thanks,

Ray