Integrating complete bond dissociation in Class II force fields via a Morse bond and cross-term reformulation

The ability to predict physical and mechanical properties of organic-based materials from a purely chemical understanding is an enduring challenge. Molecular dynamics (MD) aims to solve this challenge, however, prohibitive restrictions in the force fields used to govern the dynamics of the models remain. One such constraint is the common use of harmonic bond potentials, which provides computational efficiency but leads to the inability to model bond dissociation during large mechanical deformation simulations. Although harmonic bond potentials can be replaced with Morse bond potentials to simulate bond dissociation at large deformations, the use of harmonic cross-terms in Class II force fields prevents the complete simulation of bond dissociation. Because the accurate prediction of mechanical properties at the nanoscale plays a central role in integrated computational materials engineering (ICME) efforts, a new functional form for Class II force fields that allows for complete bond dissociation is needed. In this study, a new functional form of Class II cross-terms is established and benchmarked on a variety of organic-based crystalline, semi-crystalline, and amorphous materials. The results show that the new cross-terms provide accurate and stable MD property predictions.