[gmx-developers] Re: pppm

Jason de Joannis jdejoan at emory.edu
Wed Apr 27 22:34:04 CEST 2005

Hi All,

  A few comments about pppm or p3m...

1) It is an Ewald sum.
     (with a k-space tweak to make it faster - like PME)
2) It converges.
     (can be carried out to any accuracy, just like plain Ewald and PME)
3) It might be faster than PME, although they scale the same.
     (I'm not sure there is a consensus about this in the literature)
4) There is a published k-space error formula.
     (In contrast to PME. This aids parameter selection -- fewer surprises.)


Jason de Joannis, Ph.D.
Emory University
1515 Pierce Dr, Atlanta, GA 30329
Phone: (404) 712-2983
Email: jdejoan at emory.edu

> Date: Wed, 27 Apr 2005 09:39:13 +0200
> From: Anton Feenstra <feenstra at few.vu.nl>
> Subject: [gmx-developers] pppm
> To: Discussion list for GROMACS development
>  <gmx-developers at gromacs.org>
> Message-ID: <426F41A1.10707 at few.vu.nl>
> Content-Type: text/plain; charset=us-ascii; format=flowed
> Hi,
> A while ago, David asked if anyone is still using PPPM. I just came
> across a reason not to remove it from the code. I'm comparing several
> simulation setups across Amber, Gromacs and Gromos, in forcefield as
> well as software. Amber features ewald (PME), but Gromos doesn't and
> Gromos users use P3M in stead. If only for sake of comparisons, it may
> be good to have it still in Gromacs as well (although, one may expect
> ewald or PME to make it into mainstream Gromos as well...).
> Now we're on the issue, what is the basic difference between PPPM and
> Ewald? Can one expect systematic differences between them, or should the
> results in principle be identical?
> Finally, does anyone have a viable set of parameters for PPPM that I
> could have a look at?
> --
> Groetjes,
> Anton

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