[gmx-users] Error note

[Gavin Melaugh]

I am using 4.5.5

Justin A. Lemkul wrote:
>
>
> Gavin Melaugh wrote:
>> Hi Justin
>>
>> I saw this and had a question.
>> How important is it for a charge group to be neutral?
>>
>
> It isn't.  Conventional use dictates that the charge group bear an
> integral charge.  With PME, this is not necessary.  Many force fields
> do not use charge groups at all (i.e., single-atom charge groups).
>
>> 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.
>>
>
> The only implication I can think of would be in neighbor searching. 
> If the group is large, then short-range forces may not be calculated
> accurately.  The warning from grompp was a recent addition to the
> code; if you're using an older version you may not have triggered it.
>
> -Justin
>