Q‑Force: Quantum Mechanically Augmented Molecular Force Fields

The quality of molecular
dynamics simulations strongly depends
on the accuracy of the underlying force fields (FFs) that determine
all intra- and intermolecular interactions of the system. Commonly,
transferable FF parameters are determined based on a representative
set of small molecules. However, such an approach sacrifices accuracy
in favor of generality. In this work, an open-source and automated
toolkit named Q-Force is presented, which augments these transferable
FFs with molecule-specific bonded parameters and atomic charges that
are derived from quantum mechanical (QM) calculations. The molecular
fragmentation procedure allows treatment of large molecules (>200
atoms) with a low computational cost. The generated Q-Force FFs can
be used at the same computational cost as transferable FFs, but with
improved accuracy: We demonstrate this for the vibrational properties
on a set of small molecules and for the potential energy surface on
a complex molecule (186 atoms) with photovoltaic applications. Overall,
the accuracy, user-friendliness, and minimal computational overhead
of the Q-Force protocol make it widely applicable for atomistic molecular
dynamics simulations.