Dear Lammps users,

I try to run a hyperdynamics (HD) simulation on a molecular system with Lennard Jones, coulombic and bond interactions.

According to the lammps manual :

  • In global HD a single “bond” within the system is biased on each timestep.

  • In local HD multiple “bonds” (separated by a sufficient distance) can be biased simultaneously at each timestep.

  • “hyperdynamic bonds” are pairs of atoms that are within a short cutoff distance of each other (they differ from covalent bonds defined by the bond_style command).

When I use global HD (fix hyper/global) the simulation runs correctly. But when I use local HD (fix hyper/local) the run crashes when an atom involved in a covalent bond forms a “hyperdynamic bond” (i.e. when it is found at a distance r < cutoff from an atom of the group to which the bias is applied). However, the crash does not occur when I exclude pairwise interactions between permanently bonded atoms and the biased atoms group (using neigh_modify exclude).

My questions are:

1°/ What is the reason why this error only occurs with fix hyper/local?

2°/ Since neighbor exclusions may give inconsistent coulombic energies, is there another way to prevent atoms involved in a covalent bond to be treated via the hyperdynamics biasing?

I will really appreciate your help.

Best regards