[gmx-users] Electrostatic forces

[Florian Dommert]

* Mark Abraham <Mark.Abraham at anu.edu.au> [2009-06-17 15:31:43 +1000]:

> Florian Dommert wrote:
>> * Mark Abraham <Mark.Abraham at anu.edu.au> [2009-06-17 14:14:22 +1000]:
>>
>>> Florian Dommert wrote:
>>>
>>>> However I am very confident and in case of success, that there will be
>>>> soon an error estimate for the Ewald Sum available, which will be 
>>>> the first
>>>> step to the an implementation a tuning routine for the SPME 
>>>> paramters to achieve optimal
>>>> balance between performance and accuracy ;)
>>>
>>> I've already implemented a version of mdrun that actually computes  
>>> the  RMS error in the force components under PME, and am planning to  
>>> release  it soon.
>>
>> That is very nice to hear, how do you compute the error ? By comparing  
>> to an
>> Ewald Sum ?
>
> Holding beta fixed, I compare force components with those from a  
> converged real-space summation and high Fourier grid density &  
> interpolation order.

So you have to perform a very costly simulation for every system, when
you gather the reference force ? And which beta do you choose, because
if you take the right choice you can decrease the computational cost
extremely. So theoretically at first you have to find the right beta by
sampling through the corresponding parameter space with a fixed
Interpolation order and grid size. In the optimal range a change of beta
within 0.1 will yield a difference in the error of about 10-1 this trend
continues around +/- 0.5 of the optimal value for beta.

Flo

>
> Mark
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-- 
Florian Dommert
Dipl.-Phys.

Institute for Computational Physics
University Stuttgart

Pfaffenwaldring 27
70569 Stuttgart

Tel: +49 - 711 / 6856-3613
Fax: +49 - 711 / 6856-3658

EMail: dommert at icp.uni-stuttgart.de
Home: http://www.icp.uni-stuttgart.de/~icp/Florian_Dommert

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