Molecular dynamics treatment of torsional interactions accompanied by dissociation

When three atoms in a bend sequence move into a linear configuration, any torsional angle involving those three atoms becomes undefined and its Cartesian derivatives singular. In molecular dynamics simulations, this is most likely to occur during and after a bond‐breaking process, leading to spuriously large torsional forces and energies which invalidate the simulation. By including appropriate bend angle switching functions in torsional interaction terms, one may approach the linear bend limit in a well‐defined manner and make torsional forces vanish around this limit, as expected on physical grounds. Although this expense can be greatly reduced by observing that any internal force must not move the center of mass of the particles involved. Several approximations explored in this paper can reduce this effort even further.