[gmx-users] how to build up fixed connections? how to simulate no electrostatics?

van Bemmelen J.J.M.vanBemmelen at student.TUDelft.NL
Wed Aug 15 20:12:48 CEST 2007

Hi all,

As a side note: although I also have some trouble figuring out what
Nicolas Schmidt is exactly trying to do, I find the question "what to do
to totally switch the electrostatics off?" to be quite intriguing. It is
my understanding that when you simply set rcoulomb=0, this actually
means an infinite cutoff. This is only of real use with pbc=no when
simulating in vacuo.

So can it be done in standard GROMACS? Can you set the mdp-parameters in
such a way, that GROMACS simply skips the electrostatics calculation
altogether, thereby saving valuable computer time in systems without
charges? Or will GROMACS simply detect that there are no charges
whatsoever in the system, and automatically skip all the Coulomb
calculations? Or will GROMACS always calculate the electrostatics, even
if there are no charges present, and simply fill in zeroes for all
charges throughout the entire calculation?

Just being curious. :-)


>> Still: Though I thought I don't have to specify the 
>> electrostatics-section since my molecule doesn't have any 
>charges (or 
>> does it???), what to do to totally switch the electrostatics off?
>You should be reading section 7.3 of the manual closely and 
>making these 
>choices actively, with reference to earlier in the manual 
>where needed. 
>You'll need to understand well how both this other software 
>are doing the calculation in order to duplicate the ensemble averages.

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