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Re: [ESPResSo-users] zero angle (full angle)

From: Dudo
Subject: Re: [ESPResSo-users] zero angle (full angle)
Date: Thu, 16 Apr 2015 17:02:25 +0200

Hi Ulf,

well, I'm pretty sure the Espresso with current definition of bond angle won't allow creating a zero angle (or full angle, doesn't matter).
You may set phi0 to whatever value, it will always end up with an angle in between pi/2 and pi..
It's a good remark however, that I wrongly defined the shift which should have been introduced as cosine of the value at least.
However, it won't resolve the problem with defining two bond angle potential simultaneously which Espresso seems to dislike at the moment.

Kind regards

On Thu, Apr 16, 2015 at 4:08 PM, Ulf Schiller <address@hidden> wrote:

On 16/04/15 14:44, Dudo wrote:
> Hi,
> I'm trying to implement a zero angle potential with minima at 0 or 2*pi
> respectively.

How would you decide whether the angle is in [0,pi] or [pi,2*pi] ?

> For this I just added a phase shift into the former angle_harmonic.hpp
> potential:
> cos_phi = scalar(vec21, vec31) / (vec21_magn * vec31_magn) -
> (3.141592653589793238462 / 2.000000000000000);

This does not seem to make sense. cos_phi should be in the range [-1,1].

> However, in my model I would need also flat angle and right angle
> definitions.

For zero angle cos_phi=1, for right angle cos_phi=0, for flat angle


Dr Ulf D Schiller
Centre for Computational Science
University College London
20 Gordon Street
London WC1H 0AJ
United Kingdom

Ing. Dusan Racko, PhD
Polymer Institute of the Slovak Academy of Sciences
Dubravska cesta 3
845 41 Bratislava, Slovak Republic
tel: +421 2 3229 4321

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