[gmx-users] twin range and switched cutoffs energy differences

David Osguthorpe David.Osguthorpe at uchsc.edu
Fri Feb 22 18:04:19 CET 2008

On Thu, Feb 21, 2008 at 02:16:39PM +1100, Mark Abraham wrote:
> David Osguthorpe wrote:
> >Hi,
> >
> >I am having a problem understanding the GROMACS implementation of cutoffs
> >and switching functions - at least Im getting results I cant make sense of.
> Have you read manual sections 4.1.5 and 7.3.9? There are some salient 
> points there.

Yes - I have read those sections - and when I implemented switching functions
many years ago I got some idea of what to expect in the difference between a straight
cutoff and switched function.
The real issue is the large difference in coulombic energy - are you saying from the parameters Ive
given I should expect such a large difference in coulombic energy - these are
both truncating the coulomb potential so I dont see it as a question of whether the
coulombic energy is missing the significant long range interactions greater then
the cutoff.
These are just single point computations from the same coordinates - so the creation of fake charges/dipoles
should be identical.



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