[gmx-users] Surface tension calculation for organic monolayer

[David van der Spoel]

On 07/07/16 16:06, gozde ergin wrote:
> Dear users,
>
> I simulated three different systems in cubic box and calculated their surface tension as shown below;
>
> 1. Pure water , surface tension = 61.5 mN/m
> 2. Water with 3M NaCl salt, surface tension = 66.5 mN/m
> 3.Water surface covered with cis-pinonic organic, surface tension = 63.5 mN/m
>
> For system 1 and 2, the results are almost correct however the result for system 3 is not correct.
>
> Cis-pionic is an surface active molecule and should lower the surface tension.
> However in my simulations I could not capture this trend.
> I used GAFF force field and LINCS for the constraints.
> Does anyone has any idea?
> Or is there anyone that calculated the surface tension for organic coated surfaces with GAFF force field?
>
> Thanks
>
Maybe you should consider pH effects? Since this is an acid I would 
guess part of these are deprotonated in solution, did you consider the 
pK? You probably need to mix different amounts of protonated and 
deprotonated molecules and plot the surface tension as a function of the 
protonation state.

-- 
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
spoel at xray.bmc.uu.se    http://folding.bmc.uu.se