Re: [gmx-users] genbox problem with micelle

2007-06-04 Thread Martin Höfling
If you have the center coordinates and your cell has a good radial symmetry, i 
would just write a script, checking the distance of each water to the center 
and then skipping everything below the radius of your cell.

Cheers
Martin
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Re: [gmx-users] genbox problem with micelle

2007-06-04 Thread David van der Spoel

Alif M Latif wrote:

Dear GROMACS users and developers..
 
I'm trying to run MD simulation on a micelle structure, which i've built 
using Packmol. The problem is when i use genbox to solvate the system 
using SPC water, the water came inside the micelle, and my simulation 
didn't produce any significant changes to the structure (the behavior of 
lipids which are lipophilic should squeezed the water molecules outside 
the micelle structure). I'm wondering if i can tell genbox not to put 
water molecule inside the micelle...can i?.. :-p
 
Thanks 4 reading...any comments and suggestion will be greatly appreciated..
 
A third alternative would be to increase the vdw radii, by copying 
vdwradii.dat to your working directory and increase the water radius.


--
David.

David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
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phone:  46 18 471 4205  fax: 46 18 511 755
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[gmx-users] genbox problem with micelle

2007-06-03 Thread Alif M Latif
Dear GROMACS users and developers..

I'm trying to run MD simulation on a micelle structure, which i've built using 
Packmol. The problem is when i use genbox to solvate the system using SPC 
water, the water came inside the micelle, and my simulation didn't produce any 
significant changes to the structure (the behavior of lipids which are 
lipophilic should squeezed the water molecules outside the micelle structure). 
I'm wondering if i can tell genbox not to put water molecule inside the 
micelle...can i?.. :-p

Thanks 4 reading...any comments and suggestion will be greatly appreciated..

Alif


   

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Re: [gmx-users] genbox problem with micelle

2007-06-03 Thread Mark Abraham
 Dear GROMACS users and developers..

 I'm trying to run MD simulation on a micelle structure, which i've built
 using Packmol. The problem is when i use genbox to solvate the system
 using SPC water, the water came inside the micelle, and my simulation
 didn't produce any significant changes to the structure (the behavior of
 lipids which are lipophilic should squeezed the water molecules outside
 the micelle structure). I'm wondering if i can tell genbox not to put
 water molecule inside the micelle...can i?.. :-p

genbox just uses vdw radii for different atom types to generate volumes
that exclude waters. If your micelle (and I presume from the above that
you have a micelle that is lipid-inside-surface water-outside-surface) has
interstices that are large enough to admit waters, then genbox will place
them there.

Probably, an energy minimization of the micelle in vacuo will see it
contract so that the lipids are pretty much close-packed, and hopefully
this density will also be close to that for the micelle in solution.
Alternatively, or if there are still holes that admit waters, you can make
the radii of your lipid C and H atoms larger for the purposes of genbox
using a modified gromacs/share/top/vdwradii.dat. Be careful later with the
gentleness of your minimization and equilibration schemes else you'll
generate large structural changes and thus bad contacts and LINCS errors,
etc.

Otherwise, you could get out a molecule visualization program like VMD,
find the waters inside and delete them (you could script this with VMD,
too).

There's also a lesson here to look at your structure before you simulate
to see that it looks how you expect it to. If you'd seen these waters, and
knew for some reason that it would take longer than your simulation time
to form an equilibrated micelle by excluding these waters, then you'd have
known not to bother with this simulation, and fixed your problem without
spending computer time needlessly.

Mark

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