Using shake with charge on O and massless site

Hello,

I would like to use the pair style lj/cut/tip4p/long. I understand that this pair style automatically generates a massless dummy site just as in TIP4P and essentially moves the charge on the O atom to the massless dummy site for the coulombic calculation.

I am using a model that has charge on both the O atom and the massless dummy site, and I would like to change the source code (pair_lj_cut_tip4p_long.cpp) slightly to accommodate this model. Do you have any suggestions on how I can do so?

Thanks,

Jo

Hello,

I would like to use the pair style lj/cut/tip4p/long. I understand that
this pair style automatically generates a massless dummy site just as in
TIP4P and essentially moves the charge on the O atom to the massless dummy
site for the coulombic calculation.

I am using a model that has charge on both the O atom and the massless
dummy site, and I would like to change the source code
(pair_lj_cut_tip4p_long.cpp) slightly to accommodate this model. Do you
have any suggestions on how I can do so?

‚Äčthat is not as simple as you might think. the /tip4p/ styles inherently
assume, that there are only 3 LJ sites and 3 charged sites.

the easiest way to implement your model is to use 4 explicit sites, set the
mass of the massless site to a tiny value (say 1.0e-10) and use fix
rigid/small instead of shake.

axel.‚Äč