[gmx-users] Gel Phase in DMPC using Berger force field ??

[Jochen Hub]

Hi Steffen,

thanks a lot for your reply.
> -what are your VdW cutoffs? Berger lipids absolutely need the 0.8/1.4 nm
> twin range cutoff for working properly. Are you using PME for
> electrostatics?
>   
I used a LJ-cutoff at 1.0nm. That's what was used for the original 
Berger-Paper (*O Berger, O Edholm and F Jähnig, */Biophysical Journal/ 
72: 2002-2013 (1997). Shouldn't this be all right?

And I used PME (which was indeed not used in the original work.

> -how did you set up the pressure coupling?
>   
I used weak coupling (tau=1.0ps)

> -900 waters are not really much, the head groups will probably interact
> with their mirror images due to pbc. Try a lot more (thought about
> 10000?) for having a "real" bilayer in a solution.
>   
I also tried with more water, the gel phase did not appear either.

> >From my experience, the Berger lipids are well defined for a specific
> temperature, but if you go up/down the temperature scale, they are not
> really following the experimental values/phase behaviour. By the way:
> experimental data on lipid order parameters varies considerably
> throughout the complete literature, so don't rely onto that too much as
> well.
> Sorry for giving more questions than answers, but that's the shitty part
> with lipid bilayers in MD...
> Steffen
>   
Thanks again,
Jochen



-- 
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Jochen Hub
Max Planck Institute for Biophysical Chemistry
Computational biomolecular dynamics group
Am Fassberg 11
D-37077 Goettingen, Germany
Email: jhub[at]gwdg.de
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