Implicit Membrane Question

Hello all,

Currently, I’m interested in trying to run a fairly simple implicit membrane simulation using LAMMPS. Essentially, this would entail applying mild positional restraints to the membrane protein I’m studying, as well as defining a “belt” around the protein with a different dielectric constant to reflect the membrane’s different electrostatic character.

I am already familiar with the various restraining commands in LAMMPS, including fix spring, fix restrain, etc, and I believe I understand how to define a belt region using the corresponding built in command as well. I also see there is an option to change the dielectric constant, which appears to do what I need, however I still have some questions about combining these features:

1.) The page describing the dielectric command is quite terse, and so it seems that once a dielectric is defined, it is applied throughout the entire simulation box by default. As a result, I was wondering if there is a way to combine various geometric commands in LAMMPS to restrict the modified dielectric constant to a roughly cubical subregion of the total simulation box?

2.) Would it be consistent to use the dielectric command if I am also using an implicit solvent force field to account for the water interactions? Or would this be over-correcting? Obviously I can test some of this through direct simulation once I have things set up, but I was wondering if there was any way to have some insight about this a priori.

Thanks,
Tom Allen

Hello all,

Currently, I'm interested in trying to run a fairly simple implicit
membrane simulation using LAMMPS. Essentially, this would entail applying
mild positional restraints to the membrane protein I'm studying, as well as
defining a "belt" around the protein with a different dielectric constant
to reflect the membrane's different electrostatic character.

I am already familiar with the various restraining commands in LAMMPS,
including fix spring, fix restrain, etc, and I believe I understand how to
define a belt region using the corresponding built in command as well. I
also see there is an option to change the dielectric constant, which
appears to do what I need, however I still have some questions about
combining these features:

1.) The page describing the dielectric command is quite terse, and so it
seems that once a dielectric is defined, it is applied throughout the
entire simulation box by default. As a result, I was wondering if there is
a way to combine various geometric commands in LAMMPS to restrict the
modified dielectric constant to a roughly cubical subregion of the total
simulation box?

​no. ​

Someone (you?) would have to code a fix or alternate pair

style that applied the dielectric constant in that manner

(as a function of spatial position). Maybe a scale factor

on the Coulombic forces (for which dielectric is a pre-factor)

could be applied on one sub-style of a pair hybrid calculation.

Steve