[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 21:16:45 CEST 2007

Erik, thanks for the quick and clear answer!

Of course I should have known in advance that you guys have thought of
everything, and even implemented separate loops for every single type of
interaction that can come into play. ;-)


>Date: Wed, 15 Aug 2007 20:49:46 +0200
>From: Erik Lindahl <lindahl at cbr.su.se>
>Subject: Re: [gmx-users] how to build up fixed connections? how to
>	simulate no	electrostatics?
>To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>Message-ID: <E5C2CE7B-7E43-4509-8431-17FAB484A92E at cbr.su.se>
>Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>Hi Jeroen,
>Just set the charges to zero - then the program will automatically  
>detect it and use LJ-only loops everywhere.
>On Aug 15, 2007, at 8:12 PM, van Bemmelen wrote:
>> 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. :-)
>> Greetings,
>> Jeroen

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