[gmx-users] Dielectric is essentially 1?
spronk at its.caltech.edu
Fri Aug 12 02:48:16 CEST 2005
I have a protein-membrane system in which there are some charges in the
membrane. I am using ffgmx with PME long-range electrostatics, and I
haven't done anything with epsilon_r in my mdp files.
Would it be correct to say that in nonpolarizable force fields,
membranes have dielectric constants of 1, as opposed to 2 or 4, which
people often quote as a typical dielectric for membrane or protein
environment? Or course, in a real system, the Coulombic energy between
two charges is reduced when they are in some medium. But this effect
arises from polarization in the intervening molecules and/or
reorientation of intervening dipoles (such as water), right? So in a
system in which atoms are not polarizable (at least for ffgmx), and in
a bilayer that doesn't have water nearby for screening, the dielectric
is essentially 1? The energy between two charges in the membrane, as
calculated by the force field, is *not* any different than if they were
in a vacuum, right? I'm just making sure that I really understand the
force field terms.
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