[gmx-developers] ewald shift

[Harold Park]

Dear Berk:

I'm not sure how well the Wolf methods work for liquid systems, though  
apparently there have been some tests to show that it works well.  I  
do not know enough to say much on this point.  We are looking at  
crystalline ionic solids, which is what the method was initially  
developed for.  Thanks for your suggestion for the shifted Coulomb  
option - we will explore this.

Dear Rossen - I read the Fennell paper carefully, and the corrected  
form they utilize appears to be more robust and conserves force and  
energy at the cut-off - we will definitely implement their form  
instead.  Thank you very much for this reference!

Regards to both of you,

Harold

>
> Message: 2
> Date: Sat, 15 Aug 2009 21:18:27 +0200 (CEST)
> From: hess at sbc.su.se
> Subject: Re: [gmx-developers] ewald shift
> To: "Discussion list for GROMACS development"
> 	<gmx-developers at gromacs.org>
> Message-ID: <49431.81.234.234.16.1250363907.squirrel at mail.sbc.su.se>
> Content-Type: text/plain;charset=iso-8859-1
>
> Hi,
>
> But that is what I meant.
> A plain cut-off lead to serious artifacts,
> at least for liquid systems. In water you get very strong dipole- 
> dipole
> anti-correlation/correlation at the cut-off radius. This effects
> increases (!) with increasing cut-off distance.
> My thesis has an example of this.
> In liquid systems plain cut-off are almost not used anymore.
> Referees will probably reject work done with a plain cut-off.
> Reaction-field is better, but even that is mostly replaced by PME.
>
> For something as rigid as a crystal it might work.
> Shifted Coulomb is available in Gromacs with the mdp option
> coulombtype = shift
>
> Message: 3
> Date: Sat, 15 Aug 2009 22:13:20 +0200
> From: Rossen Apostolov <rossen at cbr.su.se>
> Subject: Re: [gmx-developers] ewald shift
> To: Discussion list for GROMACS development
> 	<gmx-developers at gromacs.org>
> Message-ID: <4A8716E0.2030701 at cbr.su.se>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
>
> You might want to check the Fennell potential method, which is an
> extension of Wolf and improves the force discontinuity at cutoff:
> Fennell, C. J.; Gezelter, J. D. J Chem Phys 2006, 124, 234104 and
> Kikugawa et al., J Comput Chem. 2009 Jan 15;30(1):110-8.
>
> Another alternative you might want to try is the isotropic periodic  
> sum
> method, Wu X, Brooks BR,  J Chem Phys. 2005 Jan 22;122(4):44107. You
> should be careful though if you use it to simulate interfaces.

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