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

[Jussi Lehtola]

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
-- 
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Jussi Lehtola, FM, Tohtorikoulutettava
Fysiikan laitos, Helsingin Yliopisto
jussi.lehtola at helsinki.fi, p. 191 50632
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Mr. Jussi Lehtola, M. Sc., Doctoral Student
Department of Physics, University of Helsinki, Finland
jussi.lehtola at helsinki.fi
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