[gmx-users] rlist and rcoulomb

Swarnendu Tripathi stripath at kent.edu
Thu Oct 21 22:26:29 CEST 2010

Dear gromacs users,

In section 4.6.3 of gromacs 4 manual it says ``... the interactions between
pairs that do not fall within rlist but do fall within max(rcoulomb,rvdw)
are computed during neighbor search (NS), and the forces and energy are
stored separately, and added to short-range forces at every time step
between successive NS.''

Now I find that if I use rlist (= rvdw) = rcoulomb then I only have Coulomb
(SR) values in the md.log file but if I use rlist (= rvdw) < rcoulomb then I
get both Coulomb (SR) and Coulomb (LR) values in the md.log. In both cases I
have assigned vdwtype=user and also rcoulomb=user for a tabulated potential
that I use.

Now, my question is how in the second case when rlist < rcoulomb I am
getting the Coulomb (LR) values in md.log? Particularly, I want to know how
the Coulomb (LR) is calculated? Is it calculated in the same way as Coulomb
(SR) and simply denoted as  Coulomb (LR), since rlist < rcoulomb? Or, in
this case it is suggested that I should always use rlist=rcoulomb.

Any suggestion is appreciated and thanks in advance.

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