A well-behaved theoretical framework for ReaxFF reactive force fields

In recent work, we have presented a new ReaxFF formulation with a superior conservation of energy in reactive molecular dynamics simulations. The key ingredient in the approach involved the tapering of bond order and bond distance discontinuities using Hermite polynomials. This Communication extends the previous formulation by alleviating additional sources of numerical instability in the original formalism. These "numerical pathologies" are rooted in the counting of lone-pair electrons, the sum of bond orders between atoms that form a valence angle, and the definition of a torsional potential. Based on a theoretical analysis, new functions that mitigate these limitations are designed and validated. The extent of their transferability with previous parameterizations is discussed. The new enhancements provide further gains in numerical stability to facilitate exploration of reactive energy landscapes.