Dear all LAMMPS user,
As written in the manuals, the dielectric command is used to reduce the strength of the interaction.
Supposed that I want to simulate the behavior of NaCl in the water tank where there’s an electric field,
since the medium is water, so I set the dielectric value to 80,4.
The question is, do have to include the water molecules in the simulation too?
Are the water molecules have been represented by the dielectric, so I don’t have to include any water molecule?
Thank you
Best regards,
Steven Lee
Dear all LAMMPS user,
As written in the manuals, the dielectric command is used to reduce the
strength of the interaction.
Supposed that I want to simulate the behavior of NaCl in the water tank
where there's an electric field,
since the medium is water, so I set the dielectric value to 80,4.
The question is, do have to include the water molecules in the simulation
too?
Are the water molecules have been represented by the dielectric, so I don't
have to include any water molecule?
this is much more a question about simulation methodology than about
LAMMPS. you should thus discuss this with your adviser/superviser and
consult textbooks and the relevant literature.
using scaled coulomb as an approximation for the solvent is *very*
crude model. for example it doesn't include a representation of the
solvation shell that forms around ions. there multiple variants of
implicit solvent models with different levels of detail.
my guess is that you will have to include explicit water molecules in
your simulation, and then you have to leave the dielectric constant at
its default value of 1.
axel.
Dear Sir Axel,
Thank you for your reply.
However, there is something that still confuse me.
Supposed that I want to simulate the behaviour of salt ions in the water,
the force interactions are LJ and coulomb.
About the coulombic force, do I have to include the water dielectric (80.4, since the media is water) in the input script,
or just leave the dielectric constant at 1?
Is there an algorithm in LAMMPS that automatically recognize the standard coulombic force using various kind of material (molecules)? Thank you
Best regards
Steven Lee
Dear Sir Axel,
Thank you for your reply.
However, there is something that still confuse me.
Supposed that I want to simulate the behaviour of salt ions in the water,
the force interactions are LJ and coulomb.
About the coulombic force, do I have to include the water dielectric (80.4,
since the media is water) in the input script,
or just leave the dielectric constant at 1?
i already answered that. you have to use 1, since you are simulating
water molecules in a vacuum.
changing the dielectic constant models the screening effect due to
atoms that are *not* there. but in order to properly model an implicit
solvent, some more work needs to be done (e.g. you need to model
viscosity and brownian motion from the solvent imposed on the embedded
particles).
please take some time and study the relevant text book knowledge on
the subject and/or discuss with your adviser. this is really basic MD
stuff and not particularly specific to LAMMPS.
Is there an algorithm in LAMMPS that automatically recognize the standard
coulombic force using various kind of material (molecules)? Thank you
this question makes no sense at multiple levels.
axel.