[lammps-users] angle style harmonic


I'm a phD student in the university of Strasbourg, France.

First of all, thank you very much for LAMMPS. I'm really enjoying using it.

I have a several question concerning 'angle style - harmonic':

1. Why after calculating the sin (s) you write s=1/s.

2. I don't understand the calculation of the forces. Does the matrice 'a' represent the dynamical matrice?

   how did you calculate it?

3. I want to use this harmonic potential but to make a difference between positive and negative angles.

   In order to calculate the energy, I think I can calculate sin(theta) with the vectorial product, and then take

   theta=acos(c) for positive values of sin(theta) and theta=-acos(theta) for negative values. But, I don't know

   what to do with the functions that calculates the forces? do I need to change them also?

   thank you ,


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I think the 1/s is just bookkeeping. You get the forces by
(carefully) differentiating the energy expression with respect
to each of the 3 atoms. I don't recall the details off the top
of my head, but you should be able to re-derive it.