[gmx-users] 'constraints' directive and water

[Alex]

That was always my default impression, but from looking into e.g. 
tip4p.itp i somehow got the idea that water _is_ affected by 'constraints'.

Yes, whenever I have hydrogens in the system (aside from water), I 
always set 'h-bonds', which, if you recall my old 'meh' regarding 
constraints, suggests that I have accepted your view for computational 
efficiency. :)  This certainly answers my question, thank you.

Alex


On 3/27/2018 1:11 PM, Justin Lemkul wrote:
>
>
> On 3/27/18 3:10 PM, Alex wrote:
>> Hi all,
>>
>> Some of my simulations run with a time step of 2 fs and 'constraints' 
>> set to 'none'. Everything runs perfectly fine, but with such a time 
>> step, do you usually set constraints to 'h-bonds'? I know I should be 
>> looking at literature for this, but just wanted to get a basic idea 
>> on whether people do this.
>>
>
> Normally constraining bonds to H is required to get stable integration 
> with dt = 2 fs. Water is a different matter; it is held rigid with 
> SETTLE and is not under the influence of the "constraints" keyword.
>
> -Justin
>