Open Force Field infrastructure automates robust parameter fits. The Open Force Field (OpenFF) Initative is an academicindustrial partnership aiming to advance the science and software infrastructure required to build the next generation of molecular mechanics force fields. OpenFF software infrastructure includes modern, automated frameworks for force field parameter assignment via direct chemical perception . In contrast to most force fields, where an atom is first assigned an atom type based on its chemical environment, in chemical perception the force field parameters are assigned directly from chemical substructures (defined by SMIRKS patterns). Importantly, this direct assignment significantly reduces the number of force field parameters, and facilitates their rapid and robust training through force field optimisation techniques. The ForceBalance software is employed for fitting of bonded and non-bonded parameter sets against quantum chemical and/or experimental datasets. OpenFF-Evaluator 20 provides a highly scalable framework for evaluating physical properties, and their gradients, based on the provided force field parameters. Evaluator interfaces with ForceBalance to enable the training, and at-scale testing, of force field non-bonded parameters against curated condensed phase physical property data, including mixture properties .