From: Jeffrey Potoff (jpotoff_at_chem1.eng.wayne.edu)
Date: Wed Feb 16 2011 - 22:18:57 CST
Yes, the bilayers were electrically neutral at all times.  You can start 
with just the bilayers in water.  Once you get a stable system you can 
remove some of the water and replace with the ions of your choice.  
Sometimes with these kinds of simulations you need to run1000-100000 
steps with a very small time step (<0.5 fs) to get rid of all the rattle 
errors.
Regards,
     Jeff
On 2/16/2011 6:51 PM, snoze pa wrote:
> Hi Jeffrey,
>
>  Thank you very much for the note and the paper in J. Phys. Chem. B, 
> 2010, 114 (41), pp 13249–13254. Actualy I am trying your system with 
> POPC membrane.
>
> In page 2, para 2, It is mentioned in your paper that:
>
> "After the 10 ns equilibration period, 13 Ca2+ ions (≈0.1 M) were 
> introduced into the confined region with 26 Cl- to maintain charge 
> neutrality. Reference calculations used 13 Na+ and 13 Cl-."
>
> Shall I assume that the membrane was treated neural during 
> equilibration process. I will re-run the simulation with 1fs time step 
> to check the problem.
>
> Thank you and Regards
> S
>
>
>
> On Wed, Feb 16, 2011 at 2:58 PM, Jeffrey Potoff 
> <jpotoff_at_chem1.eng.wayne.edu <mailto:jpotoff_at_chem1.eng.wayne.edu>> wrote:
>
>     Try running a short simulation with a timestep of 0.5-1.0 fs.
>
>
>
>     -- 
>     ======================================================================
>     Jeffrey J. Potoff jpotoff_at_chem1.eng.wayne.edu
>     <mailto:jpotoff_at_chem1.eng.wayne.edu>
>     Associate Professor                       Wayne State University
>     Department of Chemical Engineering and Materials Science
>     5050 Anthony Wayne Dr                     Phone:(313)577-9357
>     Detroit, MI 48202                         Fax:  (313)578-5815
>     http://potoff1.eng.wayne.edu
>     ======================================================================
>
>
-- ====================================================================== Jeffrey J. Potoff jpotoff_at_chem1.eng.wayne.edu Associate Professor Wayne State University Department of Chemical Engineering and Materials Science 5050 Anthony Wayne Dr Phone:(313)577-9357 Detroit, MI 48202 Fax: (313)578-5815 http://potoff1.eng.wayne.edu ======================================================================
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