[gmx-users] How do Charge Groups work?

Gale, Ella ella.gale at imperial.ac.uk
Thu Jun 29 11:48:33 CEST 2006

-----Original Message-----
From: gmx-users-bounces at gromacs.org on behalf of X.Periole
Sent: Wed 6/28/2006 7:29 PM
To: Discussion list for GROMACS users
Subject: Re: [gmx-users] How do Charge Groups work?
>> I had a system where I have no charges in it, but I do 
>>have Lennard-Jones non-bonded interactions. I've noticed 
>>that I get different values for the Lennard-jones 
>>interaction energy differs depending how I split the 
>>system up into charge groups (as the charge group concept 
>>is kinda abitrary in a system with no charges), this can 
>>not be right surely? 
>> As I understood it the charge groups were used to help 
>>compile the neighbour lists, but what I want is all the 
>>atoms within my cut-off radius to be in my pair-list (for 
>>that atom). Is there an option to ignore the charge 
>>groups? I find I get bigger Lennard-Jones interactions if 
>>I put my whole system into a charge group that if I split 
>>it up, but I need to split it up for my larger systems. 
>>Is there a way to increase the maximum number of charge 
>>groups? And is this a good idea?

>>You should check the manual for the option allowing a atom
>>base cutoff, I am not sure it actually exist.
>>A crude way to fix it would be to define each atom as a
>>seprate charge group.

Hi Xavier, thanks for the help.

I tried putting all the atoms in different charge groups, but then I get no Lennard-Jones' Interactions. I'm using a cut-off potential and my Lennard-Jones interactions are included as type 1 interactions with combination rule 1. Any ideas? 


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