[gmx-users] plain cutoff coulomb

[Mark Abraham]

Cheong Wee Loong, Daniel wrote:
> Hi all,
> 
>  
> 
> This seems like a really simple and silly question, but I have read 
> through the manual and the archives and can’t seem to find anything 
> about it.
> 
>  
> 
> If I were to set coulombtype = cutoff, g_energy will still calculate 
> Coul-LR term which suggests that Gromacs calculates some long range 
> correction term for the coulomb interactions beyond the cut-off 
> rcoulomb.  But I can’t seem to find any explanation on how the 
> interactions beyond rcoulomb is calculated when not using Ewald or PME.  
> Can anyone enlighten me? 

GROMACS uses twin-range cutoffs, so the LR term exists when coulombtype 
= cutoff, rlist > rcoulomb, and is updated on nstlist steps, or 
something similar. Search for "twin-range" in the manual.

Mark