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Re: [ESPResSo-users] Tabulated angle potential in Espresso

From: Axel Arnold
Subject: Re: [ESPResSo-users] Tabulated angle potential in Espresso
Date: Fri, 16 Dec 2011 16:43:03 +0100
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On Thursday 15 December 2011 10:40:15 Javier Ramos wrote:
> Dear Espresso users,
> I am trying to use a tabulated angle potential (variant 2 in the section
> 5.3.7 of the user guide). I have two questions.
>      i) Does the angle potetial zero corresponds to the polymer is this
> position: (p1)-(p2)-(p3)?

Yes, if you mean the stretched position, where all particles are in a line.

>     ii) It is not clear for me which is the scaled length that I need to
> use for the forces. Following the explanation in the non-bonded
> tabulated potential I am assuming that the second column has to be built
> as F(theta) = - Vprime(theta) / theta where Vprime is the derivate of
> V(theta) respect to theta and theta is the angle between p1,p2 and p3
> particles. is that right?

According to the User's guide, no. It says only that the forces are scaled 
with the inverse length of the connecting vectors, which is what is required 
due to the angle. What you therefore give is the magnitude of the force on one 
of the two outer particles, multiplied by the distance of the particle to the 
center particle.


JP Dr. Axel Arnold
ICP, Universit├Ąt Stuttgart
Pfaffenwaldring 27
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609

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