Dear Everyone,

We are using classical potential energy (e.g. Class2) where the energy function is described by the atom positions only and it has many cross terms between bond, angle, dihedral and improper.

I am wondering that are the force between pairs of atoms still along the line connecting the pair atoms even when many-body potential are used? Since the atoms are described only by points, not by the detail core and electronic clouds structures.

Can anyone please recommend some reference papers on the classical force fields and force calculation?

Thank you very much,

Lili Zhang

Dear Everyone,

We are using classical potential energy (e.g. Class2) where the energy

function is described by the atom positions only and it has many cross terms

between bond, angle, dihedral and improper.

I am wondering that are the force between pairs of atoms still along the

line connecting the pair atoms even when many-body potential are used? Since

the atoms are described only by points, not by the detail core and

electronic clouds structures.

Can anyone please recommend some reference papers on the classical force

fields and force calculation?

what you describe is a purely classical mechanical problem. as you can

easily see from describing molecular motions/geometries with a

z-matrix, bond, angles, and dihedrals are independent degrees of

freedom and thus separable, i.e. you can convert positions or forces

between the two coordinate systems. that is always possible. however,

that does not necessarily allow you to decompose the hamiltonian into

simple additive terms (think of quantum mechanics, where *every*

position affects the force on every atom for a varying degree). now,

it is not clear from your description what you are after, so it is

difficult to give any advice beyond suggesting to look at books on

classical mechanics and linear algebra.

axel.