[gmx-users] Hard Spheres

[devicerandom]

On 09/12/10 09:51, Sascha Hempel wrote:

> Thanks for your advice. I looked this up in the manual and experimented
> a little with the functions.
> I can not just set C6 to 0 beacause then i will keep a repulsing
> potential at long distances which will skrew with my system.
> I could use a shift or switch function to take care of that, but since i
> want some regular water in my system too this is not an option.
>
> So I am going to go with tabulated potentials.
> How "soft" do my hard spheres have to be to not cause any trouble for
> the gromacs engine?

Test different function shapes -it's not easy, and also it depends on 
your temperature and desired time step. The smaller the time step, the 
steeper/hotter you can go, but of course at the price of slower 
simulations. I had the same issue and I used a combination of Morse 
potentials, a rigid one for the repulsive part and a softer one for the 
attractive basin (I need one as well, you maybe don't).

m.

>
>>>>
>>>> Is there a way to add hard spheres to lets say a simulation of
>>>> Water
>>>> molecules without interfering into the regular water-water
>>>> interaction?
>>>>
>>>> Thanks a lot in advance,
>>>>
>>>> Sascha
>>>>
>>>> TU Dortmund
>>>> Laboratory of Thermodynamics
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