"compute dipole" for TIP4P water models

Dear LAMMPS community,

I am using the compute dipole to calculate the x,y, and z coordinates of the dipole vector of bulk-water TIP4P. After some tests, I found that the compute dipole does not know anything about the trick that tip4p styles do in LAMMPS. I wonder if someone has thought of a workaround that could take into account the displacement of the massless charge in the dipole computation (or any ad hoc correction) or if implementing a “compute dipole/tip4p” is the only way out. ( I am not considering the implementation of a real four-site model using fix rigid since I am using rerun to extract the dipole vector)

I’d really appreciate any comments or help you can provide.

Paulo Siani, Ph.D.
Università degli Studi di Milano Bicocca
Department of Materials Science

Ps. My LAMMPS version is (29 Oct 2020)

Since TIP4P is a rigid model, the dipole moment is overestimated by a constant factor. Just figure out what that factor is and scale the results and it should be correct.

I appreciate your quick response. Thank you, Axel!

The question has come up a few times before, so it didn’t take much thinking…
Just remembering to search the archive for “tip4p dipole” :wink:

FYI, I just submitted a pull request that adds a compute dipole/tip4p and compute dipole/tip4p/chunk to LAMMPS


Thank you very much for taking the time to implement it!
All the best!