fix property/atom command

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1

Hi,

I am trying to simulate dipoles with explicit solvent molecules and try to observe the effects in an electric field. I want the solvent molecules not to be dipoles

Can I add dipole movement to a few atoms in the simulation ( keep the atom_style atomic) so as to have point dipoles, using the fix property/atom command.

If yes can you please explain how

Regards

Nishanth

2

Hi,
I am trying to simulate dipoles with explicit solvent molecules and try to
observe the effects in an electric field. I want the solvent molecules not
to be dipoles

Can I add dipole movement to a few atoms in the simulation ( keep the
atom_style atomic) so as to have point dipoles, using the fix property/atom
command.

there is no need to do this. just use atom style dipole (or a hybrid
of dipole and whatever else you need) and just assign a zero dipole
moment to those atoms without.

axel.

3

Thanks for replying,
I have three problems

  1. Whenever I us pair_style dipole it says pair style dipole/cut has an error because some torque, dipole moment charge have not been specified. I seen someone ask a similar question to you in the past but I couldn’t understand the answer given by you. You suggested something like you need to chose a proper atom_style. could you explain

2)When I give zero dipole moment to dipoles does lammps take it as just spherical particles or it considers them as dipoles (separated +ve and -ve charge but with zero dipole moment )

3)what is the default charge the dipoles take if I do not specify. is it the overall charge given to the dipole ( because dipoles need to be neutral right) or just q of the +q and -q separated charges

Regards
Nishanth

4

Thanks for replying,
I have three problems

  1. Whenever I us pair_style dipole it says pair style dipole/cut has an error because some torque, dipole moment charge have not been specified. I seen someone ask a similar question to you in the past but I couldn’t understand the answer given by you. You suggested something like you need to chose a proper atom_style. could you explain

All I could say is written in the manual. Please read up on this.

2)When I give zero dipole moment to dipoles does lammps take it as just spherical particles or it considers them as dipoles (separated +ve and -ve charge but with zero dipole moment )

Neither. By default particles are point particles and if you add dipoles, they are point dipoles, not pairs of point charges.

3)what is the default charge the dipoles take if I do not specify. is it the overall charge given to the dipole ( because dipoles need to be neutral right) or just q of the +q and -q separated charges

This statement/question makes no sense. Please see my answer to 2) and think about this. It may help to read about multipoles in a textbook on electrostatics.

Axel

5

Atom_style hybrid sphere dipole

will allow you to assign point dipoles
to spherical particles. You can also
assign point charges, but those are 2
different attributes.

Steve