I modified the pair_gran_hook/hertz history style to take into account the Van der Waals adhesion force following JKR model. The model is described in this paper http://www.sciencedirect.com/science/article/pii/S002199910800572X where
Fn = F_adhesionJKR + F_damp
The simulation is able to run, but I got unreasonable results. I find it was caused by the formulation of "ccel" in LIGGGHTS that I used. Currently, I use the expression:
ccel = - F_adhesionJKR - F_damp
where F_adhesionJKR is defined to be positive when it pushes two particles toward each other.
F_damp is calculated as in original LIGGGHTS
I am confusing about this. Would you have any idea for the right expression of ccel in this case to adapt the JKR model with LIGGGHTS?
Thank you very much!