[gmx-users] Error note

Gavin Melaugh gmelaugh01 at qub.ac.uk
Thu Feb 23 13:42:36 CET 2012

Hi Justin

I saw this and had a question.
How important is it for a charge group to be neutral?

In one of my systems I model a solvent of crown ethers using an all atom
model. The smallest neutral unit comprises a CH2-O-CH2 (7 atoms). I have
used this as a charge group to and get no warnings.



Justin A. Lemkul wrote:
> RAMYA NAGA wrote:
>> Dear friends,
>> iam getting this note while doing pressure coupling of protein-ligand
>> complex. can anybody help me how to handle this??
>>  The largest charge group contains 11 atoms.
>>   Since atoms only see each other when the centers of geometry of the
>> charge
>>   groups they belong to are within the cut-off distance, too large
>> charge
>>   groups can lead to serious cut-off artifacts.
>>   For efficiency and accuracy, charge group should consist of a few
>> atoms.
>>   For all-atom force fields use: CH3, CH2, CH, NH2, NH, OH, CO2, CO,
>> etc.
> The error message explains what is wrong and how it should be fixed. 
> Charge groups should be small.  You have one that is very large.
> -Justin

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