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

[David Osguthorpe]

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.

Thanks

David