[gmx-users] When to use Dispersion Correction for Lipid Bilayers
mrshirts at gmail.com
Mon Aug 20 02:12:18 CEST 2012
Short answer -- use a dispersion correction if the force field was
parameterized to include one. Make sure you use the cutoff that the
lipid was parameterized for as well.
Long answer -- neither on nor off is correct for a lipid bilayer. A
dispersion corrections corrects for the fact that you are neglecting
the r^-6 term at long range. However, it assumes an isotropic
distribution outside the cutoff. Lipid bilayers have long range
order, so a standard dispersion correction is inappropriate. The
lipid properties will be cutoff dependent, which is not a very good
thing. See PJ in't Veld, AE Ismail, GS Grest, J. Chem. Phys. 127,
144711 (2007) for a solution, using Ewald summation for the
Lennard-Jones terms. This is in the works for Gromacs (and has been
for a while), but might still be a while because it's a little lower
on the to do list. Once methods like this are in, it will be possible
to parameterize lipids that behave correctly.
On Sun, Aug 19, 2012 at 3:16 PM, David Ackerman <da294 at cornell.edu> wrote:
> I was wondering when it is appropriate to use Dispersion Correction
> for lipid bilayers, or which setting (no, EnerPres, or Ener) is best.
> I have seen it used in some discussions, and not used in others. As
> for myself, I have simulated a DPPC bilayer. With DispCorr=EnerPres, I
> get an area per lipid of ~.615 nm^2 (whereas other reported values are
> closer to .64 nm^2) and slower diffusion than is reported. However,
> when I don't have a DispCorr term, my area per lipid becomes ~.656
> nm^2 and my diffusion more closely matches other reported values.
> So, should DispCorr be used at all for bilayer simulations, and if so,
> which type is most appropriate?
> Thank you for your help,
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