Lammps Version: Jan/2014 and Mar/2014
I have a question about the tensile test. I am using non-reactive force fields (Amber, GAFF, CVFF, PCFF, etc). Without using “fix bond/break”, these force fields do not allow bond breaking even at high elongation. The “fix bond/break” needs special bond setting (lj 0 1 1 coul 0 1 1) at least for those versions I use. Since all pair wise interactions between 1-2 atom pairs are turned off with the special bond setting during a deformation-Tensile loading, the pressure quantity would not be correct due to no interactions of all pair atoms bonded to each other.
Finally, I would like to break a bond with certain criteria. For example, if a bond length is twice longer than the equilibrium bond length during tensile deformation, the bond needs to be broken. The reason why I am considering bond breaking with non-reactive force fields is because the pressure exponentially increase at high elongation and the simulation dose not show a fracture. In order to do this kind of simulation (with non-reactive force fields and bond breaking), do I need to customize fix command (e.g., fix bond/break or something else)?
Any comments are appreciate.