[gmx-users] Why the individual interaction potentials are additive?

[Mark Abraham]

Hi,

Simply that it makes a useful physical model. If one has a gravitational
system with one body, then there's a single term in the potential; with
two, there's two terms added, etc. Electrostatics work the same way, of
course. Bonded interactions are a practical hack that recognize that
multi-body and non-nuclear effects are strong at very short range. So one
excludes the "normal" non-bonded interactions, and replaces their
contribution with whatever functional form + parameters seem to work well.
The additivity is simply intrinsic to the model. You can't multiply the
non-bonded interaction potential by the bonded one and get something
sensible :-)

Mark

On Mon, Feb 6, 2017 at 2:31 PM ibrahim khalil <ibrahim.khalil.chem at gmail.com>
wrote:

> Dear GROMACS users,
>
> I had a somewhat of a basic (or elementary) question.
>
> While doing MD simulations, we use interaction potentials that consist of
> bonded and nonbonded potential terms- then again the bonded term consists
> of some other potential terms such as bond, angle, dihedral etc.
>
> My question is-*Why the terms are additive?*
>
> Inside this book of R. LeSar, Introduction to Computational Materials
> Science, 2013, I found- the potential energy of a system can be expanded as
> a series of terms involving pair, triplets and quadriples of atoms etc. and
> we ignore the rest of the higher interaction terms.
>
> -which might explain the bonded interactions being additve.
>
> But why the nonbonded interactions are additive to the bonded ones?
> --
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