[gmx-users] SR Coulomb and LR Coulomb

[pascal.baillod at epfl.ch]

Hi,

Thank you very much, Erik and Hector, for the explanation on Coulomb SR and LR
terms (copy here below). Just to get the correct picture: 

1) How fast will coul_SR decrease from r=0 to r=rcoulomb? What kind of decrease
function do we have there?

2) Dose coul_LR slowly increase in that interval, compensating the coul_SR decrease?

3) How do things work with Generalized Reaction Field for long range
electrostatics? Is there a gradual decrease of coul_SR as in 1), with a gradual
increase of the reaction field term, or a discontinuous switch?

Thank you very much!

Pascal




On Mar 30, 2006, at 1:41 PM, Hector Martinez-Seara Monne wrote:

> Dear Gromacs users,
>
> I have what maybe is a silly question. I'm Using PME to perform my  
> calculations in bilayers and I have a set rcoulomb=1.0. What is the  
> SR coulomb and LR Coulomb energy in the log file? Can I say that LR  
> is the coulomb energy contribution of PME and SR is coulomb energy  
> contribution due to coulomb pairs interactions inside rcoulomb?

Almost - SR is the direct space coulomb interaction. This is not the  
same as the full interaction inside the cutoff, since the PME  
algorithm gradually switches off direct space interaction from r=0 to  
the cutoff, and treats the rest in reciprocal space.

Cheers,

Erik

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Pascal Baillod (PhD student) 
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Swiss Federal Institute of Technology EPFL	        Tel: +41-(0)21-693-0322
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