[gmx-users] Twin range cut-off's: rlist and rvdw

Jussi Lehtola jussi.lehtola at helsinki.fi
Wed May 27 13:36:08 CEST 2009

On Wed, 2009-05-27 at 11:00 +0200, Yan Chai wrote:
>     If my understanding above is correct, it seems that the concept or
> the algorithm of neighborlist for the twin range cut-off's in Gromacs
> is different from the original concept of Verlet neighborlist which is
> discussed in the textbook on MD simulations, for instance, in the book
> Understanding Molecular Simulation by Frenkel and Smit. The original
> algorithm of Verlet list needs rlist>rvdw in order to contain all
> particles which might have interactions. However, the twin range
> cut-off's in Gromacs with rvdw>=rlist seems to be contradict to this
> original idea of Verlet list and to miss some contribution to the
> interaction by the particles which stay between rlist and rvdw in the
> normal steps without updating the neighborlist.
>     So my question is: what is the idea for Gromacs to take such
> algorithm of twin range cut-off's?

In the twin range method [1] interactions that are in the range
rlist..rvdw are only calculated during neighborlist updates. In the mean
time they are considered to stay constant.

The idea behind this is that when r>rlist the interactions are weaker
and also vary more slowly, thus one doesn't need to be as precise in
taking those interactions into account.

[1] http://dx.doi.org/10.1002/prot.340060203
Jussi Lehtola, FM, Tohtorikoulutettava
Fysiikan laitos, Helsingin Yliopisto
jussi.lehtola at helsinki.fi, p. 191 50632
Mr. Jussi Lehtola, M. Sc., Doctoral Student
Department of Physics, University of Helsinki, Finland
jussi.lehtola at helsinki.fi

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