[ESPResSo-users] Fwd: Re: Scaling of tabulated angle potential

[Axel Arnold]

Just to have it also on the mailing list...

On 07/23/2014 01:59 PM, Vincent Ustach wrote:
> Hi Espresso-verse,
>
> I know there are a few threads of this nature already in the archives,
> but I have a clarifying question about the tabulated angle potential.
>
> I am building a coarse grained polymer from tabulated potentials
> calculated by probability densities. The backbone is composed of beads
> of type B and each B bead has one pendant group of type A. Therefore,
> I have nonbonded potentials, AB and BB bonded potentials, and BBB and
> ABB angular bond potentials.
>
> The UG states that the force must be scaled with the inverse length of
> the connecting vectors. For the angular bond potentials, do I need a 3
> dimensional map of V(r,phi) in order to calculate this? Right now I
> only have V(r) and V(phi)
>
> The part that confuses me is that if one builds the tabulated file
> like this
>
> #N_points    0    3.14159
> phi    (-dV/dphi)/r     V(phi)
> ....
> ....
>
> Then the r to use is not obvious to me.


From the code it looks like there is no 1/r in angle or dihedral
potentials. You can also test that using
tools/check_potential_and_forces.tcl, which samples force and potentials
and checks by numerical differentiation whether these are likely
correct. I think it can also work with angular potentials.

Axel


--
JP Dr. Axel Arnold
ICP, Universität Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609