[gmx-users] any help for PPPM?

[David van der Spoel]

feng chen wrote:
> Hi,
>  
>   For the past few days , we've been carrying out a simluation by using 
> PPPM , for some reason we end up with some wired pressure tensors. Based 
> on manual , it says it is not easy to calculate the full long-range 
> virial tensor with PPPM correctly, but it is possible to obtain the 
> trace. What confused us is that if one can get the trace right why 
> couldn't get correct virials? We have done some literature searches , 
> but until now still couldn't figure out why is it. So , can anyone point 
> out why we have such an issue between PPPM and virial tensor caculation 
> ? and can you give me a reference where I can
> learn more about?
>  
>  thanks in advance
>  
>  
>   Kevin
>  
The implementation of PPPM in gromacs is ancient, it is based on work by 
Luty & Van Gunsteren, 1995 or so. In order to use pressure coupling one 
would have to update the code. Hunenberger has described how to do it, 
around 2000, but we haven't come around to implement it, largely because 
we've put much more effort into optimizing PME, even though some people 
maintain that PPPM is more efficient in principle.

What it boils down to is that you're on your own when you want to use it.
-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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