[gmx-users] shake for water

[David Mobley]

Berk,

> Another question, just to be sure.
> Have you actually checked that the other code really gets the distances
> right up to 1e-12?

Yes.

> Berk
>
>> Date: Thu, 5 Feb 2009 12:03:21 -0600
>> From: dmobley at gmail.com
>> To: gmx-users at gromacs.org
>> Subject: [gmx-users] shake for water
>>
>> All,
>>
>> A quick question on constraints... I'm using TIP4P-Ew in gromacs 3.3.2
>> and am concerned with reproducing energies from another code very
>> precisely for several specific snapshots. I am doing a zero-step mdrun
>> of a setup with one small molecule and two tip4p-ew water molecules.
>>
>> Anyway, I have set the shake tolerance to 1e-12 in the mdp file, but
>> to my surprise the internal water distances are good only to 1e-06 and
>> 1e-07. Is this expected behavior? Note that I am running in double
>> precision. I assumed that, er, the distances should converge to the
>> shake tolerance.
>>
>> Thanks,
>> David
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